The Dish on Vitamin D
Today’s Dietitian
By Victoria Shanta-Retelny, RD, LD
Vol. 6, No. 12, p. 28

Fortified milk and ready-to-eat cereals are the main dietary sources of vitamin D, but don’t dismiss the sun—a little goes a long way.

The sun’s solar energy is an essential component of life; not only does it exude warmth and illuminate the sky, but its ultraviolet B (UVB) rays allow for optimal mineralization of the skeleton by initiating the synthesis of vitamin D. Sunlight is the primary source of vitamin D as there are very few food sources. All vertebrates need solar support to make vitamin D, which aids in the efficient intestinal absorption of calcium. Just as a flying buttress supports the structure of a gothic edifice, vitamin D has been assisting calcium in bone formation and structure in organisms since the existence of phytoplankton more than 750 million years ago.1 Recent research has shown that vitamin D’s function is not unidirectional. Epidemiologists are currently discovering its complex role in the prevention of not only skeletal diseases like rickets in children and osteomalacia in adults but also chronic, nonskeletal diseases such as heart disease, type 1 diabetes, osteoporosis, and some common cancers.

The skin has a large capacity to produce vitamin D3, according to an article in the American Journal of Clinical Nutrition by Michael F. Holick, PhD, MD, professor of medicine, physiology, and dermatology at Boston University School of Medicine and chief of endocrinology, metabolism, and nutrition. As we age, the ability to synthesize this nutrient diminishes by as much as 75% by the age of 70.1 The effects of sunlight should not be underestimated, however. Although aging decreases the amount of vitamin D (7-dehydrocholesterol) synthesis, the skin has such a large capacity to make vitamin D3 that even elders exposed to sunlight can achieve increased blood concentrations of vitamin D3 and 25-hydroxyvitamin D 25(OH)D.1

Diagnosing a Deficiency
The reality is that vitamin D deficiency is often undiagnosed or misdiagnosed. The No. 1 misdiagnosis is fibromyalgia.1 The best method of diagnosing adequate plasma levels is to measure a metabolite, 25-hydroxyvitamin D [25(OH)D], to determine vitamin D status.1 This metabolite is the major circulating form of vitamin D; however, this lab value is often not ordered by physicians.

The recommended adequate intake (AI) from the Institute of Medicine (IOM) in 1997 for vitamin D was determined inadequate in the 50-plus age group.2 The IOM report recommended children and adults up to the age of 50 get 200 international units of vitamin D per day, whereas the requirement for those aged 50 to 70 and 70 and older was raised to 400 and 60 international units vitamin D per day, respectively (see Table 1). The one caveat researchers uncovered was rate of exposure to sunlight. In the absence of exposure to sunlight, a minimum of 1,000 international units vitamin D per day is required for all age groups to maintain a healthy concentration of 25(OH)D in the blood.3

Skin—Natural Sunscreen
Topical sunscreen is not the culprit for vitamin D deficiency, even though research has revealed that as little as an SPF of 8 is enough to block UVB rays and decrease vitamin D synthesis in the skin. However, the fact of the matter is that most sunscreen users apply as little as 18% and no more than 35% to 50% of the recommended amount of sunscreen, and they do tan, which indicates that they are making sufficient amounts of vitamin D3 in their skin.1 It is the skin’s melanin that acts as “natural sunscreen” as protection from blistering solar radiation, especially for those living near the equator. Thus, darker-complected people who have greater amounts of melanin in their epidermis are less efficient in producing vitamin D3 than fair-skinned people. The alarming statistics reveal that dark-skinned people who never burn require 10 to 50 times the exposure to sunlight1 to produce the same amount of vitamin D3 in their skin than white, fair-skinned people who burn easily.

Global Epidemic
Vitamin D deficiency is “a global problem,” according to Carolyn Moore, PhD, RD, director of nutrition and health at the Beverage Institute for Health and Wellness in Houston. “Lack of vitamin D is a major health problem since fewer people are drinking vitamin D-fortified milk, children are not going outside as much, and a growing aging population that simply cannot synthesize vitamin D as well,” contends Moore. Her work with the health and wellness side of The Coca-Cola Company is to create food and beverage products that have added nutritional benefits. Her division recently teamed up with Cargill to launch Minute Maid Premium Heartwise orange juice, the first orange juice fortified with cholesterol-lowering plant sterols.

In Moore’s analysis of population-based nutrition surveys on vitamin D intakes in the United States in the Journal of the American Dietetic Association earlier this year, Moore points out that there is a surprisingly high incidence of vitamin D insufficiency in the United States and Canada in otherwise healthy individuals.4 In examining data from the Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994) and Continuing Survey of Food Intakes by Individuals 1994-1996, 1998 (CSFII 1994-1996, 1998), Moore’s research found the lowest intakes of vitamin D to be reported among female teenagers and adults and the highest intakes were found in male teens. In the aging population, Moore’s results showed that only 10% of older adults (aged 51 to 70) and 2% of elders (over the age of 70) met their daily vitamin D requirement with food consumption alone. Dietary supplementation did not alleviate the insufficient intake as 90% of those taking supplements still did not meet the AI.

The main dietary sources of vitamin D came from fortified milk and ready-to-eat cereals—both of which the general population was not getting nearly enough of. There’s a major problem in populations that avoid dairy products either for taste preferences or lactose intolerance (primarily African Americans, Asian Americans, and Mexican Americans). Calcium-fortified juices and juice drinks may contain up to 100 international units of highly bioavailable vitamin D per serving and are a source of vitamin D for individuals who avoid dairy products.4

Thus, the intention of Moore’s work is to “change the additive regulations” to allow for more food fortification of vitamin D. The public health coup of fortifying milk with vitamin D in the 1930s virtually eliminated rickets in the United States. Ninety-eight percent of fluid milk in the United States today is voluntarily fortified with vitamin D. What other beverages and food products can be fortified? The bottom line: “Encourage higher consumption,” Moore states. She is referring to vitamin D-fortified foods, such as milk, yogurt, juices, and cereals. People simply are not getting enough, according to the NHANES III and CSFII data, so recommending supplements (200 to 400 international units) for females over the age of 13 and males over the age of 50 is another safety net.

Fending Off Chronic Disease
Since sunlight is a major source of vitamin D, it only makes sense that people living farther from the equator and at higher latitudes would be more susceptible to chronic diseases caused by lack of this nutrient. Physiologically, various parts of the body utilize vitamin D to function properly. The heart, stomach, pancreas, brain, skin, gonads, and lymphocytes all have vitamin D receptors. The biological functions of this nutrient are so viscerally vast.

Several studies have shown successful prevention of autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis, and multiple sclerosis, when vitamin D receptors were present in activated T and B lymphocytes and macrophages. In studies using mice that were prone to these diseases, administration of vitamin D early in life staved off onset of these chronic diseases.5 Children receiving 2,000 international units vitamin D from the age of 1 on decreased their risk of getting type 1 diabetes by 80%.6

Cancer Prevention
It is believed that the hyperproliferation of cancer cells is slowed dramatically in the presence of vitamin D (1,25(OH)2D).7 Vitamin D has been implicated in cancer prevention, specifically colorectal and prostate cancer. The Journal of the National Cancer Institute published a study (2004) that found that increased consumption of vitamin D in fortified milk was related to lower risk of colon cancer.8 An arsenal of other studies have been documented on the relationship of vitamin D intake and colon cancer.

An extensive review published this year in Nutrition and Cancer highlighted 20 epidemiological studies—both case control and cohort studies—that looked at the relationship of vitamin D and colon cancer prevention. The summary of the findings revealed that dietary sources of vitamin D may be sufficient to significantly reduce the risk of colorectal cancer.9 When looking at human colon cells in test tube studies, the findings revealed that the active form of vitamin D decreases proliferation and enhances differentiation of colon cancer cells. The review also noted that the dynamic duo of vitamin D and calcium working in conjunction reduced cancer metastasis (spread) and angiogenesis (creation of new blood cells).9 At this point, there appears to be no set guidelines for vitamin D intake for the reduction of cancer.9

Bone Health Link
Research encourages adequate vitamin D intakes from infancy. For breast-fed infants who are not getting daily sun exposure, 200 international units vitamin D per day will prevent the onset of rickets, the childhood disease in which bones are malformed, soft, and weakened. At the age of 1, initiation of milk fortified with vitamin D is recommended to meet the AI requirements. Although the incidence of rickets is rare in the United States, there has been a slight resurgence secondary to inadequate feeding practices—ie, no vitamin D supplementation and delayed initiation of solid foods.

It is estimated that more than 25 million adults in the United States have or are at risk of developing osteomalacia or nonmineralization of the collagen matrix. Because the nonmineralized matrix cannot provide structural support, the risk of fracture is greater.1 Osteoporosis is most often associated with inadequate calcium intake; however, a deficiency of vitamin D also contributes to osteoporosis by reducing calcium absorption.10 Adequate storage levels of vitamin D help keep bones strong and may help prevent osteoporosis in older adults, nonambulatory individuals (those who have difficulty walking and exercising), postmenopausal women, and individuals on chronic steroid therapy.11 Vitamin D deficiency, which is often seen in postmenopausal women and older Americans,12 has been associated with greater incidence of hip fractures. In a review of women with osteoporosis hospitalized for hip fractures, 50% were found to have signs of vitamin D deficiency.11

Education Is Key
“As dietitians, we know that vitamin D is a unique nutrient in that it is synthesized from the sun and not commonly found in foods,” explains Melissa Joy Buoscio, MS, RD, CDE, consumer communication manager at the Midwest Dairy Council. By educating consumers on the natural food sources of vitamin D (eg, ready-to-eat cereals, fortified milk, salmon, cod liver oil), there will be a decrease in bone and other chronic diseases.

“One cup of milk provides 25% of the DRI [Dietary Reference Intake] for vitamin D,” according to Buoscio. That is equal to one-half of the recommended daily intake for adults between the ages of 19 and 50, one-fourth of the recommended daily intake for adults between the ages of 51 and 70, and approximately 15% of the Recommended Dietary Allowance for adults aged 71 and over.13 Be aware that the vitamin D content in milk can vary; it is often less than what the label states. That is why eating a variety of vitamin D food sources is the best recommendation. Not all dairy products contain vitamin D. Unlike milk, yogurt and cheese are not typically fortified with this nutrient.

Barriers to Adequate Intake of Vitamin D
Proper intestinal absorption is important to getting enough vitamin D. People with intestinal malabsorption syndromes, which severely affect the small intestine, such as liver failure, Crohn’s disease, celiac disease, and/or ulcerative colitis, are prone to developing a vitamin D deficiency due to poor absorption.

Lactose intolerance poses another barrier. There are dietary solutions, such as using lactose-free/reduced milk, drinking milk with meals—not alone—and/or cooking with milk in soups, puddings, and hot cereals. Nondairy options, such as salmon, mackerel, tuna fish, sardines, vitamin D-fortified fruit juice, and vitamin D-fortified soy milk, are good vitamin D substitutions to circumvent lactose intolerance.

Action Plan for Vitamin D Deficiency

Supplementation
As dietitians, we would like to think the best method for treating a deficiency would be through food, but the easiest and quickest method of treatment is supplementation with 50,000 international units vitamin D once per week for 8 weeks.3 In cases of fat malabsorption syndromes, a tanning bed or exposure to sunlight is the best bet. To fend off deficiency, experts recommend one multivitamin containing 400 international units vitamin D and a vitamin D supplement containing either 400 or 1,000 international units vitamin D.1

Weight Loss
Decreasing body fat percentage may actually help create a more bioavailable environment for vitamin D. Research has found a strong association between obesity and vitamin D deficiency.14 A study published in the American Journal of Clinical Nutrition (2000) looked at the obesity-vitamin D deficiency link. In this study, 19 white, healthy, and normal weight (body mass index [BMI] <25) and 19 white, healthy, and obese (BMI >30) subjects were exposed to UVB radiation to determine cutaneous synthesis and changes in serum concentrations of vitamin D3. Baseline blood samples were taken one hour before exposure and 24 hours after. One month later, the subjects were called back to participate in the supplementation component of the study. The subjects were asked to abstain from dairy products one week prior. Each was given an oral dose of 50,000 international units of vitamin D2. The finding revealed a greater than 50% decrease in bioavailability of vitamin D3 from the UVB exposure in the obese subjects.15

Since vitamin D is fat-soluble—whether it is consumed in the diet or captured from exposure to sunlight—it is efficiently deposited in the large body fat stores and is no longer bioavailable.15 This is most likely the reason that obese persons are chronically vitamin D deficient1—yet another case for the importance of weight management. Initial medical nutrition therapy weight-loss goals of 5% to 10% within six months can play a vital role in alleviating vitamin D deficiency—among myriad other health-related benefits.

Daily Sun Exposure
Experts recommend exposing hands, face, and arms to the sun for approximately 25% of the time it would take for the skin to become pink.1 This does more than satisfy the body’s requirement; it allows for ample storage of vitamin D for rainy and cloudy days.

As the research dictates, we are learning that vitamin D does much more than aid calcium in bone health. During infancy, AI is essential for maintaining healthy autoimmune functioning for life by staving off type 1 diabetes, multiple sclerosis, rheumatoid arthritis, and many forms of cancer. In adulthood, AI of vitamin D has been shown to decrease risk for common cancers and cardiovascular disease. This is a concrete case for promoting healthy lifestyle practice throughout the life cycle. By encouraging children and adults of all ages to be active outdoors, consume milk and other vitamin D-fortified products, and maintain a healthy body weight, dietetics practitioners can promote optimal synthesis and utilization of vitamin D. From birth to adulthood, the body functions best with an adequate reservoir of vitamin D, whether from sunlight, food sources, or supplements.

— Victoria Shanta-Retelny, RD, LD, is a practicing dietitian at Northwestern Memorial Wellness Institute in Chicago, a freelance food and nutrition writer, and a culinary spokesperson.

References
1. Holick M. Vitamin D: Importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004;79(3):362-371.

2. Holick MF. Vitamin D. In: Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, D.C.: Institute of Medicine. National Academy Press; 1997:250-287.

3. Heaney RP, Dowell MS, Hale CA, Bendich A. Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D. J Am Coll Nutr. 2003;22:142-146.

4. Moore C, et al. J Am Diet Assoc. 2004;104:980-983.

5. DeLuca HF, Cantorna MT. Vitamin D: Its role and uses in immunology. FASEB J. 2001;15:2579-2585.

6. Hypponen E, Laara E, Jarvelin M-R, Virtanen SM. Intake of vitamin D and risk of type 1 diabetes: A birth-cohort study. Lancet. 2001;358:1500-1503.

7. Holick MF. Vitamin D. The underappreciated D-lightful hormone that is important for skeletal and cellular health. Curr Opin Endocrinol Diabetes. 2002;9:87-98.

8. Biser-Rohrbaugh A, Hadley-Miller N. Vitamin D deficiency in breast-fed toddlers. J Pediatr Orthaped. 2001;21:508-511.

9. Grant WB, Garland C. Nutr and Cancer. 2004;48(2):115-123.

10. Heaney RP. Long-latency deficiency disease: Insights from calcium and vitamin D. Am J Clin Nutr. 2003;78:912-919.

11. LeBoff MS, Kohlmeier L, Hurwitz S, et al. Occult vitamin D deficiency in postmenopausal US women with acute hip fracture. JAMA. 1999;251:1505-1511.

12. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. Washington, D.C.: National Academy Press; 1999.

13. http://ods.od.nih.gov/factsheets/vitamind.asp

14. Bell NH, Epstein S, Greene A, Shary J, et al. Evidence for alteration of the vitamin D-endocrine system in obese subjects. J Clin Invest. 1985;76:370-373.

15. Wortsman J, Matsuoka LY, Chen TC, et al. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr. 2000;72:690-693.

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