Chemistry of Milk's Assignments

ID: 1-10, ISOLATION AND FRACTIONATION OF CASEIN AND WHEY PROTEIN

Milk protein concentrate (79% protein) reconstituted at 13.5% (w/v) protein was heated (90 °C, 25 min, pH 7.2) with or without added calcium chloride. After fractionation of the casein and whey protein aggregates by fast protein liquid chromatography, the heat stability (90 °C, up to 1 h) of the fractions (0.25%, w/v, protein) was assessed. The heat-induced aggregates were composed of whey protein and casein, in whey protein:casein ratios ranging from 1:0.5 to 1:9. The heat stability was positively correlated with the casein concentration in the samples. The samples containing the highest proportion of caseins were the most heat-stable, and close to 100% (w/w) of the aggregates were recovered post-heat treatment in the supernatant of such samples (centrifugation for 30 min at 10,000 × g). κ-Casein appeared to act as a chaperone controlling the aggregation of whey proteins, and this effect was stronger in the presence of αS- and β-casein.

Separation of Caseins and Whey Proteins
Old, actual and future separation techniques of the two major grops of milk proteins can be classified according to the casein pro-
pert y used for its extraction. This extraction technique can be physicochemical, biological or purely physicaI. The elderly known technique for casein separation is the physico-
chernical one. It even supports the casein definition (Gordon and Kaplan, 1972). Lowering milk pH to 4.6 leads to casein precipitation.
The precipitate is washed several times in order to reach a satisfactory degree of purification. AlI types of acid can be employed as precipitants but the most used ar hydrochloric and sulphuric acids. Because of
po or valorization of acid casein wheys, recent techniques of so called ionie acidification (Triballat, 1979; Rialland and Barbier, 1980, were recently developed. They are found on exchange of milk cations
(Na t , K+, Ca++) with protons (H+) brought by ion exchange resins. The resulting wheys have a lower mineraI content, especially the ones
coming from the Bridel process (Rialland et Barbier, 1980) which do not contain any acid anions. Another advantage of this last process is an increase of casein yield due to the retention in the curd of the main
proteose-peptone consequently of an hysteresis effect of solubility of this
component (Pierre et Douin, 1984).
Casein separation through biological processes leads to products with very different properties and therefore with different ultimate valorizations. Lactic fermentation allows lactose bioconversion to lactic acid
until pH reduction to 4.6. The obtained precipitate of casein has similar properties than the ones of acid casein. Addition of rennet to skim milk allows the splitting of K-casein fraction and so destabilize the casein
micelles. Then, coagulation takes place with releasing in the whey of caseinomacropeptide (C.M.P.). The so obtained rennet casein is very
mineralized and has all together plastic properties interesting for the sausage industry and stretching abilities used in cheesemaking. When formaldehyde is added before hot pressing, rennet casein precipitate is
transformed in a very hard plastic: galalithe. Separation of casein through physical techniques is still prospective. But, recent progresses in porous materials as those in high mechanical resistance metallic alloy or composite materials will lead to industrial
emergence of microfiltration and of ultracentrifugation for separating aIl different types of casein from skimmilk. Figure 3 schematizes a process for preparing native phosphocaseinate through ultracentrifugation of an ultrafiltration retentate as proposed by Maubois et al. (1974). Very promising results were obtained at laboratory scale regarding to yield (practically equal to theoritical maximum), composition and concentration of sediment and supernatant but equipment manufacturer partner was unable to build the required industrial continuous ultracentrifuge. Recent commercialization of mineral microfiltration membranes with pore homogeneity which can be expected· either because of use of new ceramic materials (Zr02' A1203, Csi) or because of us of high energy radiations for preparing thick screen membranes lead to envisage in the near future, that casein and whey proteins will be industrially separated by these physical techniques.

Separation of different Casein Species
The objectives of such a separation are not based on caseins themselve: as casein 46 % ; {3 casein 34 % ; K-casein 13 % but on thé
products that they allow to obtain more easily and with higher purity. Casein on which most of the efforts of separation are devoted is {3casein} Indeed, it could be used as raw material for preparing {3-casomorphin which is an heptapeptide located in 60-66 position in the sequence. This {3-casomorphin is similar to opiates or is a mediator for their synthesis which would play a main role in sleep or. hunger regulations and in insulin secretion (Mendy, 1984), that explains interest on this com-
ponent for dietetic therapy. Industrial separation of l:3 casein could be realized in the near future with techniques as microfiltration, ion exchange chromatography or continuous electrophoresis. Fragmentation in enzymatic membrane reactor could be easy but isolation of (3 casomorphin will require carrying out of new separation techniques,
probably chromatography or electrophoresis. Other casein fragments will eventually be interesting to isolate
either for their nutritional or even physiological properties, or for their
functional properties. Recently, Shimizu et al. (1984) indicated that N-terminal extremit (1-23) of .(J.slcaseinhad very good emulsifying activity and could be easily separated from a peptic hydrolysate through centrifugation.

Separation of Whole Whey Proteins
Whey is a dilute fluid containing 4 to 6 g of true proteins per liter. These proteins have excellent functional properties and a very high nutritional value due to their exceptional content in sulphur amino-acids,
in lysine and in tryptophane. Extraction of these proteins for the purpose of human nutrition is not a new finality because such a thing was already realized during making of old whey cheeses as Serac or Bruccio. But, is was only at the beginning of the Seventies that, with the development of membrane ultrafiltration, a true new whey industry was born for preparing very diversified whey protein products required by downstream food industries (Maubois, 1982). Membrane ultrafiltration offers possibility to prepare a large range of whey protein concentrates (W.P.c.) with protein content from 35 to 85 %. The main functional advantages of W.P.c. are:
~. solubility aIl over the pH scale,
- high water retenti on capacity,
- gelification ability,
- foaming ability.
Mainly, cheese wheys, but also casein wheys in a lower degree, contain
residual non centrifuge able lipids which are responsible of opalescence of the liquid. Most of these residual lipids are phospholipoproteins
(sphingomyeline, phosphatidylcholine and phosphatidylethanolamine)
coming from the fat globule membranes. Concentrated at the same rate than proteins during ultrafiltration, their presence in W.P.c. can limit market openings for sorne utilizations as the ones taking advantages of
foaming functionality. They are also limiting ultrafiltration fluxes and
efficiency of downstream fractionations and fragmentations. These lipoproteins could be specifically separated on industrial scale, in the near future, either by using microfiltration technique as proposed by Piot et al. (1984) or by using physico-chemical processes as the one recently developed by Fauquant et al. (1985) and which is based on aggregation of lipo-
proteins during a moderate heat treatment in presence of calcium ions.
Valorization of the se so-extracted lipoproteins will be easy because of
their excellent emulsifying capacities.
Removal of whey residual lipids is, for us, strictly necessary before any trying of separation of whey proteins through chromatography. It is  probably because this absolutely required step was not observed that industrial scale-up of Spherosil RP process has met so known difficulties.
Indeed, whey lipoproteins have very marked amphoteric and amphiphilic
characteristics which lead to a strong adsorption on all porous materials.
Consequently, this adsorption brings fouling or even "poisoning" of ion
exchange resins which becomes irremediable because of physico-chemical
limits of cleaning acceptable by these materials. Application of anion
exchange chromatography to defatted whey could allow, at the beginning,
secure preparation of W.P.C. with a proteinjT.S. ration near 90-95 %
(Malige, 1982) then by varying eluting conditions (use of pH or ionie
strength gradients for example) obtention of the different whey proteins.


ID: 12-20, ESTIMATION OF MILK PROTEINS

Protein is one of the main constituents of milk along with fat, lactose and water. Proteins are comprised of individual amino acids linked together by peptide bonds. There are 20 amino acids that are common to most living organisms. The different protein molecules are folded into complex structures and perform a range of functions in liquid milk.

Proteins are an important component in the nutritional value of milk, with liquid milk typically containing around 3.5% protein. Based on relative solubility, dairy proteins are divided into casein (contained in colloidal micelles) and whey proteins. There are four different caseins (αs1, αs2, β and κ-caseins) and they comprise around 80% of total milk protein. There are four principal whey proteins (α-lactoalbumin, β-lactoglobulin, bovine serum albumin, immunoglobulins) that together comprise around 20% of total milk protein. Besides these main proteins there are numerous minor proteins. The determination of protein content of milk and milk products is an important process that underpins the international trade in dairy products. The distinction between methods for determination of protein quality for nutrition purposes and chemically defined protein is important. In this fact sheet we refer only to the latter.

Methods for the determination of proteins in milk 

can be divided into three broad types:

1. Determination of total nitrogen

2. Direct protein determination

3. Indirect protein determination1

Each of these methods has advantages and

disadvantages; all are currently in routine use.

Determination of Total Nitrogen

Nitrogen is an important component of protein, and each protein has a unique nitrogen content. For more than a century, food analysts have determined the protein content of foods by determining the total nitrogen content and then calculating the protein content by using a suitable “nitrogen conversion factor”. This factor is determined according to the amount of nitrogen in the protein amino acid sequence. The analysis method for determining total nitrogen content may involve chemically digesting or, alternatively, combusting the sample, and converting the resulting material to a form that allows the total nitrogen to be measured. The total nitrogen value is converted to total crude protein using a nitrogen conversion factor of 6.38 for milk proteins and 6.25 for milk based infant foods. True protein nitrogen is obtained by subtracting from the total nitrogen content the nitrogen content of the filtrate of a

sample treated with trichloroacetic acid. The result (true protein nitrogen) is multiplied with the conversion factor (6.38) and gives the true protein content. The so-called Kjeldahl method and Dumas method, which are current international standards, respectively use the chemical digestion and combustion approaches. The advantage of these methods is that they have high reliability and accuracy. A disadvantage is that they require dedicated laboratory equipment and skilled staff which makes them expensive and time-consuming to carry out. Using these methods, around 95% of nitrogen in milk is found to be present as proteins, with the remainder as non-protein nitrogen sources such as urea.

Direct Protein Determination

Besides measuring the total nitrogen content, it is also possible to quantify specific protein components. A variety of methods are available for protein component determination.

a. Dye-binding assays utilise dyes that specifically bind to proteins. By measuring the intensity of the dye colour, which depends on the protein concentration, the protein content is determined.

b. Chromatographic methods involve separating the intact proteins based on their physical properties such as size, electrical charge or hydrophobic/hydrophilic properties and then measuring the relative amounts of each. There are several different types of chromatography methods available such as size-exclusion chromatography, ion-exchange chromatography, reverse phase chromatography and size exclusion chromatography. Once the proteins are separated, there are various ways in which they can be detected, e.g. by using ultraviolet, fluorescence or mass spectroscopy detectors. Calibration with appropriate commercially available protein standards allows quantitation. It is also possible to quantify individual amino acids chromatographically following thorough chemical digestion of the intact proteins. Using the ratios of selected marker amino acids that have been shown to be more common in casein or whey proteins, the whey and casein contents of milk and milk products can be estimated.

c. Electrophoresis is the separation of proteins by charge using an electric field. In order to make sure that basic and acidic proteins migrate in the same direction in the electric field, the proteins are heat-denatured in the presence of sodium dodecylsulfate (SDS). SDS binds to the hydrophobic parts of the proteins exposed upon denaturation, resulting in an almost equal relation between negative charge and molecular mass for basically every protein. In a polyacrylamide gel, every protein thus migrates during application of the electrical field a distance that is determined by its molecular mass. After separation, the individual protein bands are quantified by dye binding.

d. Immunology relies on using the interaction between an antigen and its corresponding antibody. This methodology is very suitable for the quantification of minor proteins.

To ensure accuracy for each of these methods suitable stable protein standards are important. These are commer-

cially available and a robust quality assurance procedure is essential to ensure long term accuracy for any protein

analytical methodology.

Indirect Protein Determination

Spectroscopic methods can be carried out rapidly at low costs in a production environment, but rely on calibration

to a chemical or reference method to ensure consistency. Thanks to robust and well validated ISO/IDF standard methods as listed in the bibliography, it is possible to anchor them to validated reference assays on specific products. Near and mid infrared spectroscopy are in widespread use for both liquid and solid dairy products in production laboratories and independent testing laboratories alike

ID: 21-35, GENETIC POLYMORPHISMS OF MILK PROTEIN

Extensive studies on the qualitative and quantitative aspects of milk proteins in more than 100 mammalian species have demonstrated that the protein content varies from 1 to 20% between different species and within the same species of different genetic backgrounds under different environmental conditions. The milk of all species so far analysed contains an acid-precipitable fraction, commonly known as casein, and an acid-soluble fraction known as the whey protein or milk serum protein. Gel electrophoretic

techniques have been used to reveal the identity of several types of caseins and whey proteins and to establish the presence of homologous proteins across several species. The discovery of two electrophoretically distinct forms of ~-lactoglobulin by Aschaffenburg and Drewry (1955) initiated very active research in the field of genetic polymorphism of milk proteins in several countries around the world. Research activity from different teams has contributed significantly to knowledge on the biochemistry, molecular and population genetics, properties of milk proteins and their associations with production traits. The purpose of this chapter is to present an overall picture of our present knowledge on the genetic polymorphisms of milk proteins in the following areas: methods of identification, number of variants already identified, differences in amino acid sequence, genetic basis, geographical and breed distribution, relationships with production traits, milk composition and milk quality. For obvious economic reasons, most of the research has been directed towards the bovine and, to a lesser extent, to the caprine species. Hence, most of the information given in this chapter pertains to milk of those two species.

ID: 36-50, FACTORS AFFECTING FATTY ACIDS COMPOSITION OF MILK

The predominant fatty acids in milk are the long-chain fatty acids myristic, palmitic and stearic. These saturated fatty acids account for 75 % of the total fatty acids, with a further 21 % occurring as monounsaturated fatty acids of which the most prevalent is oleic acid. Only 4 g/lOO g of the milk fatty acids are polyunsaturated, occurring mainly as linoleic and linolenic acids. All milk fatty acids are derived, almost equally, from either de novo synthesis or directly from preformed fatty acids in the diet. There are four main dietary sources of fatty acids: forages, oilseeds, fish oil and fat supplements. The digestive tract exerts a profound influence on the fate of dietary fatty acids. The short-chain saturated free fatty acids are absorbed through the walls of the rumen or abomasum into the bloodstream. The medium- and longer-chain saturated fatty acids pass into the small intestine, diffuse across the membrane wall where they are incorporated into lipoproteins and enter the bloodstream via the lymphatic system. The majority of unsaturated fatty acids are extensively hydrogenated in the rumen. However, recent work has shown that the levels of certain saturated fatty acids can be reduced and the levels of oleic, linoleic and linolenic fatty acids increased by feeding oilseeds rich in mono- or polyunsaturated fatty acids. In addition, work reported here has confirmed that eicosapentaenoic and docosahexaenoic acids can be transferred to milk when a diet containing fish oil is fed, but the transfer efficiencies are low.

Fatty Acid Composition and Synthesis of Milk Fat

Typically, milk produced from cows fed on a diet based on grass silage contains 

approximately 40 g fat/l, of which up to 97 % is in the form of triacylglycerol, and the 

remainder as monoacylglycerol and free fatty acids. Although the fatty acid content of milk is one of the most complex found in nature, with more than 500 different fatty acids identified (Hermansen, 1995), there are usually only considerable amounts of twelve to fifteen of these in any single fat. The predominant fatty acids in milk are the long-chain fatty acids (LCFA) myristic (14 : 0), palmitic (16 : 0) and stearic (1 8 : 0). These saturated fatty acids (SFA) account for 75g/lOOg total fatty acids, with a further 21 g/lOOg occurring as monounsaturated fatty acids (MUFA) of which the most prevalent is oleic acid (1 8 : 1). Only 4 g/lOO g milk fatty acids are PUFA occurring mainly as linoleic (1 8 : 2) and linolenic (1 8 : 3) acids. Milk fat is manufactured in the bovine mammary gland from glycerol and free fatty acids. The fatty acids are derived, almost equally, from either de nuvo synthesis from circulating acetate (C2) and P hydroxybutyrate (C4) or directly from preformed fatty acids in blood lipoproteins. De novo synthesis in the mammary gland produces the majority of the saturated fatty acids from C4 to C14 and half the palmitic acid (16:O). 

The fatty acids within the plasma lipoproteins are derived largely from digestion and absorption of dietary fat. The amounts derived from adipose tissue are variable, with the proportion changing depending on milk yield, stage of lactation and many other factors (Palmquist & Mattos, 1978; Grummer, 1991). Under normal conditions the major preformed fatty acids in the blood of ruminants are 16:0, 18 :O and 18: 1 (Duncan & Garton, 1963). Most preformed fatty acids are delivered to the mammary gland by LDL and VLDL or chylomicrons which contain approximately 10-15, 60 or 85 % triacylglycerol respectively (Table 2). Although HDL account for approximately 90% of blood lipids, they consist largely of phospholipids, cholesterol and cholesterol esters and have a very low triacylglycerol content (Christie, 1981). PUFA are not evenly distributed in the various plasma lipoprotein fractions, but tend to be concentrated in the phospholipid and cholesterol esters of the HDL (Dryden et al. 1971). Uptake of fatty acids into the mammary gland from HDL is poor (Brumby et al. 1972) and this may explain the low levels of PUFA in milk. During the passage into the mammary gland, triacylglycerol is largely or completely hydrolysed by a lipoprotein lipase (EC 3.1.1.34). There is little further modification of preformed fatty acids within the mammary gland except for extensive desaturation of medium- and long-chain SFA, particularly 18 :O (Bickerstaffe & Annison, 1968). For example, Stony (1981) reported that increased intake of 14:0, 16:O and 18:0 led to increases in the corresponding cis-MUFA in milk.

Effect of Diet on Supply of Fatty Acids

Fatty acids present in milk fat are derived either directly or indirectly from the diet. There are four main sources of fatty acids in ruminant diets, and they differ in the type and levels of fatty acids which they contribute to the diet. The sources are: 

(1) forages, 

(2) oils and oilseeds, 

(3) fish oil, 

(4) fat supplements.

Forages

Forages contribute to the supply of fatty acids in one of two ways. First, the rumen micro-organisms ferment cellulose and hemicellulose in the forage to acetate and butyrate, which are the precursors for de now synthesis of milk fat in the mammary gland, and second, forages contain low concentrations of oil (25-50 g oilkg DM depending on forage type). Despite their low oil content, forages may account for 25-35 % of total fatty acid intake in early lactation because they are usually eaten in large amounts. The fatty acids present in 

fresh grass are highly unsaturated with 60g/lOOg oil as 18:3 and a further 13 g/lOOg as 18:2 (Christie, 1981). The extent to which these PUFA survive either ensiling or drying is unclear. There is some evidence that cows fed on either fresh grass or hay have higher levels of n-3 PUFA in the milk than cows fed on grass silage (Mpelimpasakes, 1981; Hebeisen et al. 1993). Maize silage is becoming an important forage crop in the UK, and although the oil extracted from the grain contains high levels of 18 : 1 and 18:2 

(approximately 30 and 50 g/lOO g total fatty acids respectively) there is scant information on the fatty acid composition of maize silage.

Oils and oilseeds

Plant seeds store energy either as starch or in the form of oil. The fatty acid composition of seed oils varies widely and often one fatty acid predominates as a characteristic of a particular plant family. In recent years interest has focused on feeding diets containing either whole oilseeds or seed oils as a source of oleic (1 8 : l), linoleic (1 8 : 2) and a- or y-linolenic (1 8 : 3) acids. A number of workers have reported changes in the fatty acid composition of milk fat as a result of feeding various forms of rapeseed (Murphy et al. 1990, 1995~; Ashes et al. 1992; Emanuelson et al. 1992; Jahreis & Richter, 1994), soyabeans (Dhiman et al. 1991; Socha et al. 1991; Chouinard et al. 1992; Murphy et al. 19956), sunflowerseeds (Stegman et al. 1992), linseed (Ali et al. 1991; Khorasani et al. 1992) and evening primrose oil (Hermansen ef al. 1995). In general, inclusion of these oils or oilseeds in the diet of lactating dairy cows results in reductions in the levels of CK16 milk fatty acids and an increase in the levels of one or more of the long-chain fatty acids 18 : 0, 18 : 1, 18 : 2 or 18 : 3. The form in which the oil is presented to the rumen can have an effect on the fatty acid composition of milk fat. The greater the degree of protection from hydrogenation in the rumen, for example when contained within the whole oilseed, the lower the level of 18 : 1 in the milk fat and the higher the levels of 18:0 and 18:2 when compared with the extracted oil (Steele et al. 1971). Grain seeds are not usually regarded as a source of oil, but naked oats (Avena sativa var. nuda) contain 90-100 g oil/kg, almost twice as much as barley or wheat and 4&50 g/ lOOg of the oil is in the form of PUFA (Morrison, 1977). Consequently some studies have investigated the effect of feeding naked oats on fatty acid composition of milk (Martin & Thomas, 1988).

Fish Oils

Plants, unlike animals, can synthesize de now a-linolenic acid (18:3n-3), the parent 

compound of the n-3 series of essential fatty acids. Marine plants, in particular, have the 

ability to elongate and desaturate the parent compound to yield n-3 PUFA with C20 and C22 chain lengths. It is the formation of these long-chain n-3 PUFA by marine algae and their efficient transfer through the food chain to fish, that accounts for the abundance of C20 and C22 n-3 PUFA in marine fish oils. There is currently some controversy concerning the extent to which n-3 PUFA in fish oils are transferred to milk fat. Efficiencies reported in the literature range from poor, following intravenous infusion of cod-liver oil (Stony et al. 1969) to good (35-40% transfer) following post-ruminal infusion of menhaden oil (Hagmeister et al. 1988). Grummer (1991) suggests that this discrepancy may be explained because Stony et al. (1969) administered non-physiological forms of fish oil triacylglycerol directly into the circulatory system instead of incorporation of the fatty acids into intestinally synthesized lipoproteins which would occur following post-ruminal infusion. However, in a study where dairy cows were fed on diets containing cod-liver oil, there was no 20:5 or 22:6 transferred to milk fat although the levels of 20 : 0,20: 1 and 22 : 0 increased (Brumby et al. 1972). Some authors suggest that the PUFA in fish oil may not be hydrogenated in the rumen. In vitro studies where a fish oil-casein mixture (1 : 1, w/w) was incubated with rumen contents from sheep for 24 h, showed a reduction in 18: 1 (cis and trans), but no change in 20 : 5 and 22 : 6 levels (Ashes et al. 1992).

Fat Supplements

Fat supplements tend to be given as energy supplements and have been developed to 

minimize any adverse effect on fibre digestion or microbial activity in the rumen. Consequently, the fat supplements in widespread use in the UK contain predominately saturated fatty acids based on palm fatty acids or mixtures of partially hydrogenated waste fats from the human food industry. The use of tallows in UK ruminant feeds is currently limited because of the risk of transmission of factors linked to bovine spongiform encephalopathy (BSE) in cattle.

ID: 51-70, FAT SOLUBLE VITAMINS

As the name suggests, fat-soluble vitamins are a type of vitamin that is absorbed into the body through fatty tissue. The human body requires a variety of vitamins to keep working properly. There are two types of vitamins: water-soluble and fat-soluble vitamins. Vitamins are often obtained through regular food intake. Some people require or want additional vitamins provided through supplements. Though both types of vitamin are important to the body, this article focuses on the types, functions, and sources of fat-soluble vitamins.

What are Fat Soluble Vitamins?
Fat-soluble vitamins will not dissolve in water. Instead, fat-soluble vitamins absorb best when taken with higher-fat foods.
Once absorbed into the body, fat-soluble vitamins are stored in fatty tissues and liver. The body can use these stores for future use. The water-soluble vitamins are vitamins B and C.
There are four types of fat-soluble vitamins:

• Vitamin A
• Vitamin D
• Vitamin E
• VitaminK

Each type of fat-soluble vitamin promotes different functions in the body. People deficient in the fat-soluble vitamins may require supplements to boost their supply.
However, it is possible to take in too much of a fat-soluble vitamin, which could lead to toxicity and adverse reactions.
VITAMIN A
Vitamin A plays an important role in maintaining healthy vision. Without vitamin A, a person would suffer from severe vision issues.
Types
Vitamin A does not refer to one single vitamin but is a collection of compounds known as retinoids. Retinoids can be found both in the human body and in some food sources.
Functions
Vitamin A supports several functions throughout the body. Some of the most important functions it supports include vision and the immune system.
Dietary Intake
Vitamin A can be obtained through natural sources. Some sources include:

• Fish Liver Oil
• Liver of Animals
• Butter

Animal sources provide the active components to help create retinols within the human body.
Some plants also provide pro-vitamin A compounds known as carotenoid antioxidants. The most common is called beta carotene, which can be found in foods such as:

• Kale
• Carrots
• Spinach

Recommended Intake
The recommended intake of vitamin A varies by age and gender. The following are some recommended daily allowance values:

• Infants (0–12 months): 400–500 micrograms (mcg)h
• Childrenaged 1–3: 300 mcg
• Children aged 4–8: 400 mcg
• Children aged 9–13: 600 mcg
• Adult women: 700 mcg
• Adult men: 900 mcg

Deficiency
Vitamin A deficiency is not common in developed countries. However, vegetarians are at a higher risk of a deficiency because they do not get some kinds of vitamin A through their normal diet. Similarly, people in developing countries with limited food sources or people whose diet is low in meat intake may also suffer from vitamin A deficiencies. Some signs of vitamin A deficiency include:

• Hair loss
• Dry eyes
• Blindness
• Reduced Immune Function
• Skin issues

Overdose
It is possible to reach toxic levels of vitamin A. This condition is called hypervitaminosis. People who take vitamin A supplements or eat copious amounts of fish liver oils are at the highest risk. Pregnant women should not double up on their prenatal vitamins. High levels of vitamin A are harmful to a growing fetus. If a person experiences an overdose, they may experience symptoms ranging from headaches and fatigue. In severe cases, hypervitaminosis in a pregnant woman may result in a baby with birth defects.

VITAMIN D
Vitamin D is produced naturally in the human body when the skin is exposed to the sun. Vitamin D aids in bone health and development.
Types
Similar to vitamin A, vitamin D is a collective term used to describe a collection of compounds. Collectively, these are often referred to as calciferol. There are two types found naturally:

• Vitamin D-3, found in animal fats
• Vitamin D-2, found in plants, such as mushrooms.

Function
Once vitamin D is absorbed into the bloodstream, the liver and kidneys change calciferol into calcitriol, the biologically active form of vitamin D. When used in the body, vitamin D performs two major roles:

• Bone Maintenance
• Immune System Support

Dietary Sources
Vitamin D absorption is one of the only arguments for a person exposing large, unprotected areas of skin to the sun. When exposed regularly, people can actually absorb enough rays to produce vitamin D to function properly, without need for supplements. However, many people do not spend hours in the sun. When people do, they are also often covered in sunscreen and clothing. As a result, a person is not likely to absorb as much vitamin D through sunlight alone. Instead, people can obtain vitamin D through some food sources, including:

• Fish oil
• Fatty fish
• Mushrooms exposed to ultraviolet light
• Fortified dairy products

Recommended Intake
Recommended daily values of vitamin D vary by age, though not by much. Some general guidelines indicate the following daily values:

• Infants (0–12 months): 10 mcg
• 1–70 years of age: 15 mcg
• Above age 70: 20 mcg

Deficiency
It is not very common for a person to develop vitamin D deficiency. When it happens, most cases involve older adults or people who have been admitted to the hospital for extended amounts of time.
Some people are at a higher risk of developing a vitamin D deficiency. These include:

• Obese people
• People with dark skin tones
• Older adults
• Those who get limited sun exposure
• People with chronic conditions

Some of the most common signs and symptoms of vitamin D deficiency include:

• Increased bone fractures
• Weakend immune system
• Weakened muscles
• Impaired healing
• Soft bones
• Hair loss
• More prone to infections
• Tiredness

Overdose
Toxic levels of vitamin D rarely occur. They are most likely to occur in people who take too many vitamin D supplements. An overabundance of vitamin D in the body can lead to a condition called hypercalcemia. This condition is marked by excessive levels of calcium in the blood.
When hypercalcemia occurs, a person may experience:

• Nausea
• Headache
• Weight loss
• Damage to heart or kidneys
• Reduced appetite
• High blood pressure

VITAMIN E

Vitamin E is an antioxidant that can help the body destroy free radicals. Free radicals are unstable atoms that may cause the formation of cancer cells. As such, vitamin E could play an important part in preventing cancer.

Types

Vitamin E is broken down into eight different types, with the two main kinds being tocopherols and tocotrienols. Tocopherol contains the most abundant form of vitamin E.

Functions

As an antioxidant, vitamin E protects fatty tissues from free radicals that can cause cancer. Some water-soluble vitamins, such as C and B, help aid vitamin E's functions.

In higher doses, vitamin E can also function as a blood thinner.

Dietary Sources

Vitamin E is most abundant in seeds, vegetable oils, and nuts. Some of the best sources of vitamin E include:

• Wheat germ oil
• Sunflower seeds or oil
• Hazelnuts
• Almonds

Recommended Intake

Similar to vitamin D, recommended daily values for vitamin E vary by age. Here are some of the breakdowns of recommended daily values:

• Infants aged 0–6 months: 4 milligrams (mg)
• Infants aged 7–12 months: 5 mg
• Children aged 1–3 years: 6 mg
• Children aged 4–8 years: 7 mg
• Boys aged 9–13 years: 11 mg
• 14 years old and above: 15 mg
• During lactation: 19 mg

Deficiency
Vitamin E deficiency is extremely rare in otherwise healthy individuals. Those with specific illnesses that block the liver from absorbing vitamin E are most at risk.
Symptoms of deficiency include:

• Trouble walking
• Muscle weakness or tremors
• Vision issues
• Numbness

There are also several long-term health issues that can result from vitamin E deficiency, including anemia and heart disease.
Overdose
It is nearly impossible for a person to overdose on vitamin E through natural sources. Most people who experience an overdose do so because of taking vitamin E supplements. However, people taking blood thinners may be more prone to overdose. In high doses, vitamin E may actually increase the risk of a person developing cancer.

VITAMIN K
Vitamin K helps the body form blood clots. This necessary function prevents a person from bleeding out from small scratches.
Types
Vitamin K has a variety of types. The two most common groups are:

• Vitamin K-1, found in plant sources
• Vitamin K-2, found in animal sources

There are additional man-made types of vitamin K.
Function
The main role that vitamin K plays in the body is blood clotting. However, vitamin K can also help with:

• Reducing risk of heart disease
• Bone health

• Reducing the buildup of calcium in the blood

Dietary Sources

Vitamin K-1 and K-2 are found in a variety of sources. Some of these sources include:

• Kale
• Liver
• Spinach
• Parsley
• Butter
• Egg yolks

Recommended Intake

Unlike the other vitamins mentioned, vitamin K recommended values are thought of as adequate intake. When a supplement is measured in adequate intake, it means there is less evidence to support the specified amount. Some recommended adequate intakesinclude:

• Infants aged 0–6 months: 2 mcg
• Infants aged 7–12 months: 2.5 mcg
• Children aged 1-3 years: 30 mcg
• Children aged 4–8 years: 55 mcg
• Children aged 9–13 years: 60 mcg
• Children aged 14-18 years: 75 mcg
• Adult women: 90 mcg
• Adult men: 120 mcg

Deficiency

Vitamin K is not stored in as great an amount in the body as vitamin A or D. This can lead a person to experience a vitamin K deficiency very quickly. If a person has a vitamin K deficiency, they have a greater risk of excess bleeding and reduced bone density that can lead to fractures.

Overdose

Naturally occurring vitamin K has no known issues with overdose. Synthetic vitamin K-3, however, may cause overdose when taken in excess. In general, vitamin K is considered safe to consume.