Vitamin D: Is the Real Risk Too Much or Too Little?

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Vitamin D: Is the Real Risk Too Much or Too Little?

By Jack Challem

 

Copyright 2002 by Jack Challem, The Nutrition Reporter™

All rights reserved. This article originally appeared in Let's Live

magazine.

 

http://www.nutritionreporter.com/New_Look_at_Vitamin_D.html

 

Sure, it's possible to overdose on vitamin D, as dietitians commonly

warn. But the bigger problem may be just the opposite: many people

do not get enough of the " sunshine vitamin. " The reason? They just

aren't spending much time in the sun.

 

The body makes its own vitamin D, in large but safe amounts, when

the skin is exposed to sunshine. And some foods, such as salmon,

herring, mackerel, and fortified organic dairy, contain moderate

amounts of it. But commuters, office workers, or people who stay at

home - and mostly indoors - don't make much vitamin D. As a result,

they may be at an increased risk of cancer, diabetes, and

osteoporosis.

 

Those aren't the only contradictions when it comes to vitamin D.

Although it is considered a vitamin, it is also a hormone. Vitamin

D3, its most biologically active form, regulates the growth and

development of many different types of cells in the body.

 

And because of its hormonal effects, scientists have been trying to

develop synthetic anticancer drugs that mimic the chemical structure

and activity of vitamin D. Although plain old vitamin D is still

preferrable, the research has fostered a better understanding of the

vitamin and our need for it.

 

A New Anticancer Vitamin?

 

The activity of vitamin D in the body depends on the vitamin D

receptor (VDR), a particular type of cell structure that influences

the behavior of numerous of genes affecting cell growth, immunity,

and bone development. The VDR itself is controlled by the VDR gene.

However, defects in the VDR gene limit its ability to efficiently

use vitamin D.

 

The effect is somewhat like a row of falling dominos. Because people

with VDR defects cannot properly utilize vitamin D, they are

essentially at risk of being deficient in vitamin D, even if they

consume " normal " amounts of it. This genetic bottleneck impairs the

activity of genes that ultimately depend on the VDR.

 

Recent studies have found that VDR defects are fairly common. It is

possible that such defects had few consequences when early humans

spent considerable time outdoors. Today, these defects can increase

the risk of some types of cancer, diabetes, and osteoporosis.

 

In a recent study, Kay W. Colston, M.D., of St. George's Hospital

Medical School, London, analyzed variations in the VDR gene among

181 women with breast cancer and 241 women without the disease. One

particular variation in the VDR gene was found in almost half of the

women with breast cancer. Having that gene doubled their risk of

breast cancer.

 

Colston's study is consistent with a large body of research on

vitamin D and cancer. Researchers at the University of North

Carolina, Chapel Hill, have reported that women with low blood

levels of vitamin D were five times more likely to develop breast

cancer.

 

Other human studies, as well as those with animals and cells, have

found that vitamin D may protect against colon, pancreatic, and

prostate cancer.

 

Diabetes and Multiple Sclerosis

 

Vitamin D also appears to influence immunity and lower the risk of

some types of auto-immune diseases. Recently, Elina Hypponen, Ph.D.,

of the Institute of Child Health, London, and her British and

Finnish coresearchers reported that adequate intake of vitamin D may

reduce the risk of type 1 (insulin-dependent) diabetes,

characterized by an autoimmune attack on the insuling-producing

pancreas.

In tracking the health of more than 10,000 infants and children,

Hypponen found consistent intake of vitamin D-containing supplements

reduced the risk of type 1 diabetes by 88 percent, compared with no

supplementation. Irregular supplementation was almost as protective.

 

Even people at risk of type 2 (noninsulin-dependent) diabetes might

benefit from vitamin D. Researchers at University Hospital, Aachen,

Germany, found that a VDR defect, slightly different from the one

involved in breast cancer, increased the risk of type 2 diabetes by

more than three and one-half times.

 

Vitamin D might also reduce the risk of multiple sclerosis (MS), an

autoimmune disease that attacks the delicate sheaths surrounding

nerves. The prevalence of MS tends to increase in populations living

farther from the equator, where there are seasonal fluctuations in

sunlight - and exposure to sunlight. In an animal study, Colleen E.

Hayes, Ph.D., of the University of Wisconsin, Madison, has shown

that vitamin D suppresses the some of the inflammation underlying

MS.

 

Vitamin D Needed for Bones

 

People with MS lose bone mass three to seven times faster than

healthy people, and they are 10 times more likely to experience

fractures, both potential signs of vitamin D deficiency.

 

While calcium is generally regarded as the principal bone nutrient,

vitamin D is required for calcium assimilation into bone.

 

Rickets, a nutritional deficiency disease, results from inadequate

intake or production of vitamin D. It was common among infants and

children from the industrial revoltion until the 1940s. Before the

discovery of vitamin D, doctors recommended cod liver oil and

sunshine to prevent the bone-softening consequences of rickets.

 

Although rickets has, in modern times, been considered rare, it may

be reemerging. Shelley R. Kreiter, MD, of the Wake Forest University

School of Medicine, Winston-Salem, N.C., recently reported in the

Journal of Pediatrics that that 15 of 30 studied infants and

toddlers had rickets in the past two years. All were African-

American and were breast fed without vitamin D supplementation. The

infants also had relatively little exposure to sunlight, which is

especially critical for dark-skinned peoples. (Dark skin filters out

ultraviolet light.)

 

Adequate vitamin D is needed during adulthood to maintain strong

bone. Meryl S. LeBoff, M.D., of Brigham and Women's Hospital,

Boston, has found that women hospitalized for hip fractions tended

to have low vitamin D levels and half of them were deficient. In a

separate study, Bess Dawson-Hughes, M.D., of Tufts University, gave

either calcium (500 mg/day) and vitamin D (700 IU/day) supplements

or dummy pills to 389 men and women ages 65 and older. People

receiving the calcium and vitamin D had impressive increases in bone

density after just one year, and the benefits continued to accrue

during the three years of the study.

 

Are Deficiencies Common?

 

The current federal dietary reference intakes for vitamin D are 200

IU daily through age 50, 400 IU from age 51 to 70, and 600 IU after

71. But many researchers believe that these levels are too low. A

study by Melissa K. Thomas, M.D., Ph.D., of the Harvard Medical

School, found vitamin D deficiencies widespread among a group of 290

patients hospitalized for a variety of disorders. Fifty-seven

percent were considered deficient, and 22 percent were " severely "

deficient.

 

It is possible that Americans' penchant breads, pastas, and pizzas

reduce absorption of vitamin D from the diet.

 

Loren Cordain, Ph.D., an expert on nutrition and human evolution,

has noted that refined flour reduces vitamin D metabolism.

Moderately high dosages of vitamin D - 400-800 IU daily,

particularly during the short days of winter - are safe for most

people.

 

Long-term intake of very large amounts of vitamin D, above 2,000 IU

daily, could lead to such side effects as demineralization of bones,

nausea, and muscular weakness. However, a simple 20-minute daily

walk in the sun stimulates the body's production of vitamin D.

 

According to the University of Wisconsin's Hayes, people living or

working in sunny climates safely produce more than 10,000 IU daily.

Ideally, it would be best to have your physician measure your blood

level of vitamin D. A normal level should be approximately 100 or so

nmol/L (nanomoles per liter of blood).

 

Finally, several recent studies have found that women who cover most

of their body for religious reasons, such as Muslims and Orthodox

Jews, risk vitamin D deficiencies. As one example, Turkish

researchers reported that veiled Muslim women had lower levels of

vitamin D compared with nonveiled women.

 

 

REFERENCES

 

Bretherton-Watt D, Given-Wilson R, Mansi JR, et al. Vitamin D

receptor gene polymorphisms are associated with breast cancer risk

in a UK caucasion population. British Journal of Cancer, 2001;85:171-

175.

 

Janowsky EC, Lester GE, Weinberg CR, et al. Association between low

levels of 1,25 dihydroxyvitamin D and breast cancer risk. Public

Health Nutrition, 1999;2:283-291.

 

Hypponen E, Laara E, Reunanen A, et al. Intake of vitamin D and risk

of type 1 diabetes: a birth cohort study. Lancet, 2001;358:1500-

1503.

 

Ortlepp JR, Lauscher J, Hoffmann R, et al. The vitamin D receptor

gene variant is associated with the prevalence of typ 2 diabetes

mellitus and coronary artery disease. Diabetic Medicine, 2001;18:842-

845.

 

Hayes CE. Vitamn D: national inhibitor of multiple sclerosis.

Proceedings of the Nutrition Society, 2000;59:531-535.

 

Kreiter SR, Schwartz RP, Kirkman HN, et al. Nutritional rickets in

African American breast fed infants. Journal of Pediatrics,

2000;137:153-157.

 

LeBoff MS, Koklmeier L, Hurwitz S, et al. Occult vitamin D

deficiency in postmenopausal US women with acute hip fracture. JAMA,

1999;281:1505-1511.

 

Dawson-Hughes B, et al. Effect of calcium and vitamin D

supplementation on bone density in men and women 65 years of age or

older. New England Journal of Medicine, 1997;337:670-6.

 

Thomas MK, Lloyd-Jones DM, Thadhani RI, et al. Hypovitaminosis D in

medical inpatients. New England Journal of Medicine, 1998;338:777-

783.

 

Cordain L. Cereal Grains: humanity's double edge sword. World Review

of Nutrition and Dietetics, 1999;84:19-73.

 

Guzel R, Kozanoglu E, Guler-Uysal F, et al. Vitamn D status and bone

mineral density of veiled and unveiled Turkish women. Journal of

Womens Health & Gender-Based Medicine, 2001;10:765-770.

 

 

The information provided by Jack Challem is strictly educational and

not intended as medical advice. For diagnosis and treatment, consult

your physician.

_________________

 

JoAnn Guest

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DietaryTipsForHBP

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