Case Study 10 Absorption Of Water Soluble Vitamins Answers

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by L. Bellows and R. Moore* (11/12)

Quick Facts…

  • Small amounts of vitamin A, vitamin D, vitamin E and vitamin K are needed to maintain good health.
  • Fat-soluble vitamins will not be lost when the foods that contain them are cooked.
  • The body does not need these vitamins every day and stores them in the liver and adipose (fat) tissue when not used.
  • Most people do not need vitamin supplements.
  • Megadoses of vitamins A, D, E or K can be toxic and lead to health problems.
  • Requirements for vitamins may be expressed in different mathematical units. Close attention should be paid to ensure that similar units are being compared.

What are Vitamins?

Vitamins are essential micronutrients your body needs in small amounts for various roles throughout the human body. Vitamins are divided into two groups: water-soluble (B-complex vitamins and C vitamins) and fat-soluble vitamins (A, D, E and K). Unlike water-soluble vitamins that need regular replacement in the body, fat-soluble vitamins are stored in the liver and fatty tissues, and are eliminated much more slowly than watersoluble vitamins. For more information on water-soluble vitamins, see fact sheet 9.312 Water-Soluble Vitamins: Vitamin B-Complex and Vitamin C.

What are Fat-Soluble Vitamins?

The fat-soluble vitamins, A, D, E, and K, are stored in the body for long periods of time and generally pose a greater risk for toxicity when consumed in excess than water-soluble vitamins. Eating a normal, well-balanced diet will not lead to toxicity in otherwise healthy individuals. However, taking vitamin supplements that contain megadoses of vitamins A, D, E and K may lead to toxicity. The body only needs small amounts of any vitamin.

While diseases caused by a lack of fat-soluble vitamins are rare in the United States, symptoms of mild deficiency can develop without adequate amounts of vitamins in the diet. Additionally, some health problems may decrease the absorption of fat, and in turn, decrease the absorption of vitamins A, D, E and K. Consult a medical professional about any potential health problems that may interfere with vitamin absorption.

Vitamin A: Retinol

What is Vitamin A

Vitamin A, also called retinol, has many functions in the body. In addition to helping the eyes adjust to light changes, vitamin A plays an important role in bone growth, tooth development, reproduction, cell division, gene expression, and regulation of the immune system. The skin, eyes, and mucous membranes of the mouth, nose, throat and lungs depend on vitamin A to remain moist. Vitamin A is also an important antioxidant that may play a role in the prevention of certain cancers.

Food Sources for Vitamin A

Eating a wide variety of foods is the best way to ensure that the body gets enough vitamin A. The retinol, retinal, and retinoic acid forms of vitamin A are supplied primarily by foods of animal origin such as dairy products, fish and liver. Some foods of plant origin contain the antioxidant, betacarotene, which the body converts to vitamin A. Beta-carotene, comes from fruits and vegetables, especially those that are orange or dark green in color. Vitamin A sources also include carrots, pumpkin, winter squash, dark green leafy vegetables and apricots, all of which are rich in beta-carotene.

How much Vitamin A

The recommendation for vitamin A intake is expressed as micrograms (mcg) of retinol activity equivalents (RAE). Retinol activity equivalents account for the fact that the body converts only a portion of betacarotene to retinol. One RAE equals 1 mcg of retinol or 12 mcg of beta-carotene (Table 1). The Recommended Dietary Allowance (RDA) for vitamin A is 900 mcg/ day for adult males and 700 mcg/day for adult females.

Compared to vitamin A, it takes twice the amount of carotene rich foods to meet the body’s vitamin A requirements, so one may need to increase consumption of carotene containing plant foods.

Recent studies indicate that vitamin A requirements may be increased due to hyperthyroidism, fever, infection, cold, and exposure to excessive amounts of sunlight. Those that consume excess alcohol or have renal disease should also increase intake of vitamin A.

Vitamin A Deficiency

Vitamin A deficiency in the United States is rare, but the disease that results is known as xerophthalmia. It most commonly occurs in developing nations usually due to malnutrition. Since vitamin A is stored in the liver, it may take up to 2 years for signs of deficiency to appear. Night blindness and very dry, rough skin may indicate a lack of vitamin A. Other signs of possible vitamin A deficiency include decreased resistance to infections, faulty tooth development, and slower bone growth.

Too much Vitamin A

In the United States, toxic or excess levels of vitamin A are more of a concern than deficiencies. The Tolerable Upper Intake Level (UL) for adults is 3,000 mcg RAE (Table 2). It would be difficult to reach this level consuming food alone, but some multivitamin supplements contain high doses of vitamin A. If you take a multivitamin, check the label to be sure the majority of vitamin A provided is in the form of beta-carotene, which appears to be safe. Symptoms of vitamin A toxicity include dry, itchy skin, headache, nausea, and loss of appetite. Signs of severe overuse over a short period of time include dizziness, blurred vision and slowed growth. Vitamin A toxicity also can cause severe birth defects and may increase the risk for hip fractures.

Vitamin D

What is Vitamin D

Vitamin D plays a critical role in the body’s use of calcium and phosphorous. It works by increasing the amount of calcium absorbed from the small intestine, helping to form and maintain bones. Vitamin D benefits the body by playing a role in immunity and controlling cell growth. Children especially need adequate amounts of vitamin D to develop strong bones and healthy teeth.

Food Sources for Vitamin D

The primary food sources of vitamin D are milk and other dairy products fortified with vitamin D. Vitamin D is also found in oily fish (e.g., herring, salmon and sardines) as well as in cod liver oil. In addition to the vitamin D provided by food, we obtain vitamin D through our skin which produces vitamin D in response to sunlight.

How much Vitamin D

The Recommended Dietary Allowance (RDA) for vitamin D appears as micrograms (mcg) of cholecalciferol (vitamin D3) (Table 1). From 12 months to age fifty, the RDA is set at 15 mcg. Twenty mcg of cholecalciferol equals 800 International Units (IU), which is the recommendation for maintenance of healthy bone for adults over fifty. Table 1 lists additional recommendations for various life stages.

Exposure to ultraviolet light is necessary for the body to produce the active form of vitamin D. Ten to fifteen minutes of sunlight without sunscreen on the hands, arms and face, twice a week is sufficient to receive enough vitamin D. This can easily be obtained in the time spent riding a bike to work or taking a short walk. In order to reduce the risk for skin cancer one should apply sunscreen with an SPF of 15 or more, if time in the sun exceeds 10 to 15 minutes.

Vitamin D Deficiency

Symptoms of vitamin D deficiency in growing children include rickets (long, soft bowed legs) and flattening of the back of the skull. Vitamin D deficiency in adults may result in osteomalacia (muscle and bone weakness), and osteoporosis (loss of bone mass).

Recently published data introduces a concern that some adults and children may be more prone to developing vitamin D deficiency due to an increase in sunscreen use. In addition, those that live in inner cities, wear clothing that covers most of the skin, or live in northern climates where little sun is seen in the winter are also prone to vitamin D deficiency. Since most foods have very low vitamin D levels (unless they are enriched) a deficiency may be more likely to develop without adequate exposure to sunlight. Adding fortified foods to the diet such as milk, and for adults including a supplement, are effective at ensuring adequate vitamin D intake and preventing low vitamin D levels.

Vitamin D deficiency has been associated with increased risk of common cancers, autoimmune diseases, hypertension, and infectious disease. In the absence of adequate sun exposure, at least 800 to 1,000 IU of vitamin D3 may be needed to reach the circulating level required to maximize vitamin D’s benefits.

Who is at Risk — These populations may require extra vitamin D in the form of supplements or fortified foods:

  • Exclusively breast-fed infants: Human milk only provides 25 IU of vitamin D per liter. All breast-fed and partially breast-fed infants should be given a vitamin D supplement of 400 IU/day
  • Dark Skin: Those with dark pigmented skin synthesize less vitamin D upon exposure to sunlight compared to those with light pigmented skin.
  • Elderly: This population has a reduced ability to synthesize vitamin D upon exposure to sunlight, and is also more likely to stay indoors and wear sunscreen which blocks vitamin D synthesis.
  • Covered and protected skin: Those that cover all of their skin with clothing while outside, and those that wear sunscreen with an SPF factor of 8, block most of the synthesis of vitamin D from sunlight.
  • Disease: Fat malabsorption syndromes, inflammatory bowel disease (IBD), and obesity are all known to result in a decreased ability to absorb and/or use vitamin D in fat stores.

Too much Vitamin D

The Tolerable Upper Intake Level (UL) for vitamin D is set at 100 mcg for people 9 years of age and older (Table 2). High doses of vitamin D supplements coupled with large amounts of fortified foods may cause accumulations in the liver and produce signs of poisoning. Signs of vitamin D toxicity include excess calcium in the blood, slowed mental and physical growth, decreased appetite, nausea and vomiting.

It is especially important that infants and young children do not consume excess amounts of vitamin D regularly, due to their small body size.

Vitamin E: Tocopherol

What is Vitamin E

Vitamin E benefits the body by acting as an antioxidant, and protecting vitamins A and C, red blood cells, and essential fatty acids from destruction. Research from decades ago suggested that taking antioxidant supplements, vitamin E in particular, might help prevent heart disease and cancer. However, newer findings indicate that people who take antioxidant and vitamin E supplements are not better protected against heart disease and cancer than non-supplement users. Many studies show a link between regularly eating an antioxidant rich diet full of fruits and vegetables, and a lower risk for heart disease, cancer, and several other diseases. Essentially, recent research indicates that to receive the full benefits of antioxidants and phytonutrients in the diet, one should consume these compounds in the form of fruits and vegetables, not as supplements.

Food Sources for Vitamin E

About 60 percent of vitamin E in the diet comes from vegetable oil (soybean, corn, cottonseed, and safflower). This also includes products made with vegetable oil (margarine and salad dressing). Vitamin E sources also include fruits and vegetables, grains, nuts (almonds and hazelnuts), seeds (sunflower) and fortified cereals.

How much Vitamin E

The Recommended Dietary Allowance (RDA) for vitamin E is based on the most active and usable form called alpha-tocopherol (Table 1). Food and supplement labels list alpha-tocopherol as the unit International units (IU) not in milligrams (mg). One milligram of alpha-tocopherol equals to 1.5 International Units (IU). RDA guidelines state that males and females over the age of 14 should receive 15 mcg of alpha-tocopherol per day. Consuming vitamin E in excess of the RDA does not result in any added benefits.

Vitamin E Deficiency

Vitamin E deficiency is rare. Cases of vitamin E deficiency usually only occur in premature infants and in those unable to absorb fats. Since vegetable oils are good sources of vitamin E, people who excessively reduce their total dietary fat may not get enough vitamin E.

Too much Vitamin E

The Tolerable Upper Intake Level (UL) for vitamin E is shown in Table 2. Vitamin E obtained from food usually does not pose a risk for toxicity. Supplemental vitamin E is not recommended due to lack of evidence supporting any added health benefits. Megadoses of supplemental vitamin E may pose a hazard to people taking blood-thinning medications such as Coumadin (also known as warfarin) and those on statin drugs.

Vitamin K

What is Vitamin K

Vitamin K is naturally produced by the bacteria in the intestines, and plays an essential role in normal blood clotting, promoting bone health, and helping to produce proteins for blood, bones, and kidneys.

Food Sources for Vitamin K

Good food sources of vitamin K are green, leafy-vegetables such as turnip greens, spinach, cauliflower, cabbage and broccoli, and certain vegetables oils including soybean oil, cottonseed oil, canola oil and olive oil. Animal foods, in general, contain limited amounts of vitamin K.

How much Vitamin K

To help ensure people receive sufficient amounts of vitamin K, an Adequate Intake (AI) has been established for each age group (Table 1).

Vitamin K Deficiency

Without sufficient amounts of vitamin K, hemorrhaging can occur. Vitamin K deficiency may appear in infants or in people who take anticoagulants, such as Coumadin (warfarin), or antibiotic drugs. Newborn babies lack the intestinal bacteria to produce vitamin K and need a supplement for the first week. Those on anticoagulant drugs (blood thinners) may become vitamin K deficient, but should not change their vitamin K intake without consulting a physician. People taking antibiotics may lack vitamin K temporarily because intestinal bacteria are sometimes killed as a result of long-term use of antibiotics. Also, people with chronic diarrhea may have problems absorbing sufficient amounts of vitamin K through the intestine and should consult their physician to determine if supplementation is necessary.

Too much Vitamin K

Although no Tolerable Upper Intake Level (UL) has been established for vitamin K, excessive amounts can cause the breakdown of red blood cells and liver damage. People taking blood-thinning drugs or anticoagulants should moderate their intake of foods with vitamin K, because excess vitamin K can alter blood clotting times. Large doses of vitamin K are not advised.


  • Fat-soluble vitamins: A, D, E, and K — are stored in the body for long periods of time, and pose a greater risk for toxicity than water-soluble vitamins. Fat-soluble vitamins are only needed in small amounts.
  • Beta carotene is an important antioxidant that the body converts to Vitamin A, and it is found in a variety of fruits and vegetables.
  • Inadequate dietary consumption of vitamin D, along with limited sun exposure, makes vitamin D deficiency a growing public health concern.
  • Vitamin E benefits the body by acting as an antioxidant, and research indicates that it may offer a protective effect if obtained through a diet rich in fruits and vegetables, as opposed to a supplement or multivitamin.
  • The bacteria in our gut produce vitamin K, and it is also found in green leafy vegetables.


Table 1. Recommended Dietary Intake (RDA) and Adequate Intake (AI) for Fat-Soluble Vitamins

Life Stage GroupVitamin A
Vitamin D
Vitamin E
(mcg a-TE3)
Vitamin K
   0 – 6mo400*10*4*2.0*
   6mo – 12mo500*10*5*2.5*
   1 – 3y30015630*
   4 – 8y40015755*
   9 – 13y600151160*
   14 – 18y900151575*
   19 – 30y9001515120*
   31 – 50y9001515120*
   51 – 70y9001515120*
   9 – 13y600151160*
   14 – 18y700151575*
   19 – 30y700151590*
   31 – 50y700151590*
   51 – 70y700151590*
   14 – 18y750151575
   19 – 30y770151590
   31 – 50y770151590
   14 – 18y1200151975
   19 – 30y1300151990
   31 – 50y1300151990

1As retinol activity equivalents (RAEs). 1 RAE = 1mcg retinol or 12 mcg beta-carotene.

2As cholecalciferol (vitamin D3). 10 mcg cholecalciferol = 400 IU of Vitamin D.

3As alpha-tocopherol equivalents. 1 mg of alpha-tocopherol = 1.5 IU of Vitamin E=22IU of d-alpha-tocopherol=33 IU of dl-alpha- tocopherol

4At 6 months of age, infants may be introduced to solid foods while remaining on formula or breast milk. There may be some overlap in specific nutrient requirements.

*Indicates an Adequate Intake (AI). All other values are Recommended Dietary Allowance (RDA).

Table 2. Tolerable Upper Intake Levels (UL) for Fat-Soluble Vitamins

Life Stage GroupVitamin A
Vitamin D
Vitamin E
(mg a-TE)
Vitamin K*
   0 – 6mo60025ND2ND
   6mo – 12mo60038NDND
   1 – 3y60063200ND
   4 – 8y90075300ND
   9 – 13y1700100600ND
   14 – 18y2800100800ND
   19 – 70y30001001000ND
Pregnant and Lactating
   19 – 50y30001001000ND

1At 6 months of age, infants may be introduced to solid foods while remaining on formula or breast milk. There may be some overlap in specific nutrient requirements.

2ND = not determinable due to insufficient data

*An UL for vitamin K was not established.


Advanced Nutrition: Macronutrients, Micronutrients, and Metabolism (2009). CRC Press, Taylor & Francis Group.

Advanced Nutrition and Human Metabolism (2009). Wadsworth, Cengage Learning.

Biochemical, Physiological, Molecular Aspects of Human Nutrition (2006). Saunders, Elsevier Inc.

Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2011.

Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: National Academy Press, 2000.

Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001.

Dietary Supplements: What you need to know (2011). NIH Clinical Center. Available on

Duyff, ADA . American Dietetic Association: Complete Food and Nutrition Guide. Hoboken: John Wiley & Sons, Inc., 2006. Ebook Library Web. 02 Oct. 2012.

Holick, M.F. and Chen, T.C. Vitamin D deficiency: a worldwide problem with health consequences. American Journal of Clinical Nutrition. 2008. April 87 (4): 1080S-6S.

U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th Edition, Washington, DC: U.S. Government Printing Office, December 2010.

Wagner CL, Greer FR. American Academy of Pediatrics, Section on Breastfeeding and Committee on Nutrition. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008; 122(5): 1142–1152.

* L. Bellows, Colorado State University Extension food and nutrition specialist and assistant professor; and R. Moore, graduate student. 3/02. Revised 11/12.

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vitamin E by itself is associated with overall incidence of cancer. In an earlier paper from this same study, however, Willett et al. (1983) reported that the cancer risk associated with low serum selenium appeared strongest in persons with low serum vitamin E.

Wald et al. (1984) studied 5,004 women aged 28 to 75 in Guernsey, United Kingdom, who gave blood between 1968 and 1975. The plasma was stored at -20°C. By the end of 1982, general practitioners reported 39 cases of breast cancer in women whose plasma samples were available for analysis. The stored samples for these women and samples from 78 controls were matched 2-to-1 for menopausal status, parity, family history of breast cancer, and history of benign breast disease. Vitamin E was significantly lower in cases (0.47 mg/dl) than in controls (0.60 mg/dl)—p < .025—after adjusting for age of subject and duration of plasma storage. The adjusted relative odds of breast cancer according to plasma levels of vitamin E were only meaningful below 0.5 mg/dl.

In Basel, Switzerland, between 1971 and 1973, Stähelin et al. (1984) measured vitamin E in fresh samples of fasting blood from employed men who volunteered for venipuncture. It is unclear whether or not they excluded subjects with evidence of cancer. They conducted a mortality follow-up of this cohort through 1980. Information regarding cancer in subjects who died during this 7- to 9-year period was obtained from death certificates, autopsies, and a cancer registry. Mean concentrations of plasma vitamin E for men who died with a diagnosis of cancer—notably of lung, stomach, and colon—did not differ significantly from those for age-matched men who were still alive in 1980.

In 1977, Salonen et al. (1985) collected (and stored at - 20°C) sera from a random 6.7% sample of 30- to 64-year-old people living in two provinces of eastern Finland. Deaths were ascertained through 1980, and diagnoses of cancer on the death certificate were confirmed from hospital records. Serum concentrations of a-tocopherol, selenium, and retinol were measured for 51 persons who died of cancer (18, GI tract; 15, lung; and 18, other sites) and 51 controls matched for sex, age, and number of tobacco products smoked daily. Cases did not differ significantly from controls in either mean concentration of serum a-tocopherol (4.9 and 5.0 mg/dl, respectively) or mean ratio of a-tocopherol to cholesterol (18.9 and 20.8%, respectively).  However, multivariate analysis showed a strong interaction between selenium and a-tocopherol. After adjustment for main effects, the relative risk of fatal cancer for persons in the lower tertile of selenium and of a-tocopherol levels was 11.4.

From 1971 through 1975, as part of the Honolulu Heart Program, nonfasting serum specimens were obtained (and stored at -75°C) from 6,860 men of Japanese ancestry who were born between 1900 and 1919 and lived on Oahu (Nomura et al., 1985). Subsequent cancer diagnoses were monitored by continuous surveillance of all general hospitals on Oahu and through the Hawaii Tumor Registry. After 10 years of follow-up, 284 newly diagnosed cases of epithelial cancer, all confirmed histologically, were identified: 81, colon; 74, lung; 70, stomach; 32, rectum; and 27, urinary bladder. Controls (302) were randomly selected from the examined men who did not have any of the cancers that were under study. This sampling was stratified by age group so that the age distribution of all cases combined could be matched. The mean serum concentrations of vitamin E in controls and in men with cancer of the lung, stomach, colon, rectum, and bladder were 12.3, 12.8, 12.2, 12.2, 11.6, and 12.7 mg/dl, respectively; none of the case-control differences was statistically significant.

Menkés and Comstock (1984) noted that serum vitamin E levels were significantly lower (p = .01) in 88 persons who subsequently developed lung cancer than in 76 controls matched for age, sex, date of venipuncture, and smoking history.

Animal Studies

Jaffe (1946) reported that wheat germ oil inhibited production of methylcholanthrene-induced tumors in rats. Subsequently, several investigators conducted studies to determine if vitamin E was effective in preventing sarcomas and cancers of the mouth, skin, and breast in animals, but their results have been mixed.

Haber and Wissler (1962) observed some inhibition of sarcoma formation in mice injected with 3-methylcholanthrene, but such inhibition was not found by Epstein et al. (1967), who exposed mice to 3,4,9,10-dibenzpyrene. Constantinides and Harkey (1985) reported that a-tocopherol, administered subcutaneously in a base of soya oil, produced vigorously growing sarcomas at the site of injection in 77% of animals, but they did not determine whether the effect was due to the soya oil, the vitamin E, or the combination.

Shklar (1982) noted that twice-weekly vitamin E supplementation of the diets of hamsters exposed to dimethylbenz[a]anthracene resulted in fewer,

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