Vitamin D Is For Cancer Defense

[Guest guest]

From The March 2000 Issue of Nutrition Science News

 

Nutrient Review

Vitamin D Is For Cancer Defense

by Bill Sardi

 

From time to time news reports surface about a " cancer cluster " among workers in

a building. Often the workers have been assigned to dark basement offices or

sealed clean-rooms where they must wear space-suitlike garb. After an indoor

environmental examination, investigators often are unable to correlate any

factor in the building with the cancer cases. But what if, rather than a

cancer-causing agent, the cancer cases are attributable to a missing protective

factor? Given a growing body of evidence linking cancer with vitamin D

deficiency, a question surfaces: Are indoor workers getting sufficient sunlight

to make enough vitamin D to protect them from cancer?

 

Vitamin D is formed in the skin of animals and humans by the action of

short-wave ultraviolet light, the so-called fast-tanning sun rays. Precursors of

vitamin D in the skin are converted into cholecalciferol, a weak form of vitamin

D3, which is then transported to the liver and kidneys where enzymes convert it

to 1,25-dihydroxycholecalciferol, the more potent form of vitamin D3.

 

Fat-soluble vitamin D supplements are available in two forms. Vitamin D3 is

believed to exhibit the most potent cancer- inhibiting properties and is the

preferred form of the vitamin. More than 10 substances belong to a group of

steroid compounds that exhibit vitamin D activity. Vitamin D2 (ergocalciferol),

derived from plants and yeast, is a form of the vitamin commonly added to milk

and some nutritional supplements. The first vitamin D to be discovered was a

crude mixture called vitamin D1; it is not available as a supplement.

 

Although the list of vitamin-D-rich foods is limited, it is acquired from foods

such as egg yolks, butter, cod liver oil and from cold-water fish such as

salmon, herring and mackerel.

 

Cancer Prevention

Evidence of vitamin D's protective effect against cancer is compelling. For more

than 50 years, documentation in the medical literature suggests regular sun

exposure is associated with substantial decreases in death rates from certain

cancers and a decrease in overall cancer death rates. Recent research suggests

this is a causal relationship that acts through the body's vitamin D metabolic

pathways. For instance, some evidence points to a prostate, breast and colon

cancer belt in the United States, which lies in northern latitudes under more

cloud cover than other regions during the year. Rates for these cancers are two

to three times higher than in sunnier areas.1

 

Dark-skinned people require more sun exposure to make vitamin D. The thickness

of the skin layer called the stratum corneum affects the absorption of UV

radiation. Black human skin is thicker than white skin and thus transmits only

about 40 percent of the UV rays for vitamin D production. Darkly pigmented

individuals who live in sunny equatorial climates experience a higher mortality

rate (not incidence) from breast and prostate cancer when they move to

geographic areas that are deprived of sunlight exposure in winter months. The

rate of increase varies, and researchers hesitate to quote figures because many

migrant black populations also have poor nutrition and deficient health care

that confound statistics somewhat.2

 

Although excessive sun exposure may give rise to skin cancer, researchers as

early as 1936 were aware that skin cancer patients have reduced rates of other

cancers. One researcher estimates moderate sunning would prevent 30,000 annual

cancer deaths in the United States.3

 

Vitamin D may also go beyond cancer prevention and provide tumor therapy. Much

ado has been made of pharmaceutical angiogenesis inhibitors—agents that help

inhibit the growth of new, undesirable blood vessels that tumors require for

nutrient supply and growth. Laboratory tests have shown vitamin D to be a potent

angiogenesis inhibitor.4

 

Vitamin D also works at another stage of cancer development. Tumor cells are

young, immortal cells that never grow up, mature and die off. Because vitamin D

derivatives have been shown to promote normal cell growth and maturation, drug

companies today are attempting to engineer patentable forms of vitamin D for

anti-cancer therapy.5

 

D Is for Strong Bones

Up until now, vitamin D has been better known for its ability to promote bone

strength by increasing calcium absorption. Supplemental vitamin D has been shown

to reduce hip fracture risk among elderly women when combined with supplemental

calcium. In one study of 3,270 healthy women, mean age 84, 1,634 received 1.2 g

calcium and 800 international units (IU) vitamin D3, while the other 1,636

received placebo. During the 18-month study, the supplemented group experienced

43 percent fewer hip fractures, 32 percent fewer nonvertebral fractures, and a

2.7 percent increase in bone density of the proximal femur vs. the 4.6 percent

bone density decrease seen in the placebo group.6

 

Other studies bear out vitamin D's importance to bone health, to the point where

it's now widely known that vitamin D deficiency is associated with hip

fractures, and supplementation helps. Unfortunately, not everyone is getting

enough vitamin D. A recent study reveals that about 10 percent of retirees in

Boston social clubs are vitamin-D deficient (< 15ng/mL serum vitamin D) compared

with 21 percent of hip-fracture patients at the Massachusetts General Hospital.7

So experts now suggest people take 600 IU vitamin D daily, and up to 800 IU a

day for elderly patients who do not produce vitamin D from sun exposure as

easily as they did when younger.8 A recent study showed that 37 percent of adult

hospital patients were deficient in vitamin D upon admission. Two-thirds of

these patients did not consume enough vitamin D from dietary sources.

Surprisingly, 46 percent of those who took daily multivitamins (most of which

provide 400 IU) were also in a state of deficiency.9

 

How Much Vitamin D?

The U.S. Recommended Dietary Allowance (RDA) of vitamin D is 200 IU. Yet,

studies have shown that 200 IU/day has no effect on bone status.10 Reinhold

Vieth, Ph.D., of the University of Toronto, recently published a landmark review

of vitamin D in the May 1999 American Journal of Clinical Nutrition. Vieth says

adults may need, at a minimum, five times the RDA, or 1,000 IU, to adequately

prevent bone fractures, protect against some cancers and derive other

broad-ranging health benefits.

 

Vieth says the 1989 RDA of 200 IU is antiquated, and the newer 600 IU Daily

Reference Intake (DRI) dose for adults older than 70 is still not adequate. Even

the 2,000 IU upper tolerable intake, the official safety limit, does not deliver

the amounts of vitamin D that may be optimal, Vieth says. On a sunny summer day,

total body sun exposure produces approximately 10,000 IU vitamin D per day. As a

result, concerns about toxic overdose with dietary supplements that exceed 800

IU are poorly founded, Vieth says. His review indicates a person would have to

consume almost 67 times more vitamin D than the current 600 IU recommended

intake for older adults to experience symptoms of overdosage.11 Vieth believes

people need 4,000 & shy;10,000 IU vitamin D daily and that toxic side effects are

not a concern until a 40,000 IU/day dose.11

 

Harvard researchers agree with Vieth. They suggest that older adults, sick

adults, and " perhaps all adults " need 800 & shy;1,000 IU daily. They indicate that

daily doses of 2,400 IU—four times the recommended intake—can be consumed

safely.10 Robert P. Heaney, a noted expert on vitamin D and calcium dynamics at

Creighton University in Nebraska, says that even though the recommendations for

vitamin D have recently been updated to account for increased needs among the

elderly, Vieth's review may stir policymakers to further upgrade current dietary

reference intakes. Heaney says whatever the increase in the recommended

allowance turns out to be, " it seems inescapable that it will be substantially

higher than the current values and possibly higher than nutritional policymakers

may be prepared to accept. " 12

 

Those who do follow the suggestion to consume more vitamin D may want to watch

for toxicity symptoms of headache, nausea, dizziness, vomiting, loss of appetite

and dry mouth—though these are not usually seen outside of underlying health

conditions such as kidney or parathyroid hormone dysfunction.

 

Vitamin D is not prevalent in foods. A study conducted at the Bone Research

Laboratory at Boston University School of Medicine revealed that fortified milk

may not be a reliable source of vitamin D. Only 29 percent of commercial milk

samples tested were within 80 & shy;120 percent of the amount stated on the label.

Most milk products were overfortified, and a few milk cartons contained no

vitamin D at all.13 Vitamin D milk fortification procedures vary widely from

dairy to dairy. Some dairies place their vitamin D preparations in refrigerated

storage, and others do not, which may affect the vitamin D content of the final

product.14

 

Few vitamins can provide such an array of health benefits as vitamin D. Sunshine

is still the most economical and beneficial way to improve circulating vitamin D

levels. In addition, the lack of sunlight exposure could lead to more than

thinning bones and an increased risk for cancer—there is the added benefit of

controlling cholesterol. Since vitamin D is produced naturally within the body,

technically it is a hormone. Vitamin D precursors require cholesterol for

conversion into the hormone-vitamin. Without adequate sun exposure, vitamin D

precursors turn to cholesterol instead of the vitamin. The increased

concentration of blood cholesterol during winter months and the fact that

outdoor activity (gardening) is associated with lower circulating cholesterol

levels in the summer, but not in winter, may explain geographical differences in

coronary heart disease incidence.15

 

Sunning before 10 a.m. and after 3 p.m. avoids the sun's harshest UV radiation.

People who live in areas of winter cloud cover, are homebound, or don't get

enough sun should consider naturally compounded vitamin D3 (cholecalciferol)

supplements.

 

Bill Sardi is a health journalist and consumer advocate in Diamond Bar, Calif.

His recent publications include The Iron Time Bomb (Purity Pub., 1999) and All

About Eyes Naturally (Avery Publishing Group, 2000).

 

References

 

1. Studzinski GP, Moore DC. Sunlight—can it prevent as well as cause cancer? Can

Res 1995;55:4014-22.

 

2. Angwafo FF. Migration and prostate cancer: an international perspective. J

Natl Med Assoc 1998 Nov; 90 (11 suppl):S720-3.

 

3. Ansleigh HG. Beneficial effects of sun exposure on cancer mortality. Prev Med

1993;22:132-40.

 

4. Shokravi MT, et al. Vitamin D inhibits angiogenesis in transgenic murine

retinoblastoma. Inv Oph 1995;36:83-7.

 

5. Studzinski GP, Moore DC. Vitamin D and the retardation of tumor progression.

In Watson RR, Mufti SI, editors, Nutrition and cancer. Boca Raton: CRC Press,

1996. p 257-82.

 

6. Chapuy MC, Arlot ME. Vitamin D3 and calcium to prevent hip fractures in

elderly women. New Eng J Med 1992;327:1637-42.

 

7. Neer RM. Environmental light: effects on vitamin D synthesis and calcium

metabolism in humans. Ann NY Acad Sci 1985;453:14-20.

 

8. National Academy of Sciences, Recommended Dietary Allowances, 10th ed.,

Washington, DC: National Academy Press, 1989.

 

9. Thomas MK, et al. Hypovitaminosis D in medical inpatients. New Eng J Med

1998;338:777-83.

 

10. Dawson-Hughes B, et al. Rates of bone loss in post-menopausal women randomly

assigned to one of two dosages of vitamin D. Am J Clin Nutr 1995;61:1140-5.

 

11. Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and

safety. Am J Clin Nutr 1999;69:842-56.

 

12. Heaney RP. Lessons for nutritional science from vitamin D. Am J Clin Nut

1999;69:825-6.

 

13. Holick MF, et al. The vitamin D content of fortified milk and infant

formula, New Eng J Med 1992;326:1178-81.

 

14. Hicks T, et al. Procedures used by North Carolina dairies for vitamin A and

D fortification of milk. J Dairy Sci 1996;79:329-33.

 

15. Grimes DS, et al. Sunlight, cholesterol and coronary heart disease. Q J Med

1996;89:579-89.

 

 

 

 

 

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