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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