|What You and Your Doctor Don''t Know About Vitamin D Could Kill You |
What is vitamin D?
• It helps improve muscle strength and immune function.
• It helps reduce inflammation.
• It promotes the absorption of calcium from the small intestine.
• It helps maintain adequate blood levels of the calcium and phosphate needed for bone formation, mineralization (incorporating minerals to increase strength and density), growth, and repair.
Most people get some vitamin D through sunlight exposure. It can also be obtained through the diet, but very few foods naturally contain vitamin D. These foods include fatty fish, fish liver oil, and eggs. Smaller amounts are found in meat and cheese.
Most dietary vitamin D comes from fortified foods, such as milk, juices, yogurt, bread, and breakfast cereals. Vitamin D can also be obtained through dietary supplements. Fortified foods and dietary supplements usually contain either vitamin D2 or vitamin D3. A person’s vitamin D status is usually checked by measuring the level of 25-hydroxyvitamin D in their blood serum.
Who is at Risk of Vitamin D Inadequacy?
Obtaining sufficient vitamin D from natural food sources alone is difficult. For many people, consuming vitamin D-fortified foods and, arguably, being exposed to some sunlight are essential for maintaining a healthy vitamin D status. In some groups, dietary supplements might be required to meet the daily need for vitamin D.
|1. Older adults are at risk. |
Older adults are at increased risk of developing vitamin D insufficiency in part because, as they age, skin cannot synthesize vitamin D as efficiently, they are likely to spend more time indoors, and they may have inadequate intakes of the vitamin D.
2. People with limited sun exposure are at risk.
Homebound individuals, women who wear long robes and head coverings for religious reasons, and people with occupations that limit sun exposure are unlikely to obtain adequate vitamin D from sunlight. Because the extent and frequency of use of sunscreen are unknown, the significance of the role that sunscreen may play in reducing vitamin D synthesis is unclear. Ingesting RDA levels of vitamin D from foods and/or supplements will provide these individuals with adequate amounts of this nutrient.
3. People with dark skin are at risk.
Greater amounts of the pigment melanin in the epidermal layer result in darker skin and reduce the skin''s ability to produce vitamin D from sunlight. Ingesting RDA levels of vitamin D from foods and/or supplements will provide these individuals with adequate amounts of this nutrient.
4. People with fat mal absorption are at risk.
As a fat-soluble vitamin, vitamin D requires some dietary fat in the gut for absorption. Individuals who have a reduced ability to absorb dietary fat might require vitamin D supplements. Fat mal absorption is associated with a variety of medical conditions including some forms of liver disease, cystic fibrosis, and Crohn''s disease.
5. People who are obese or who have undergone gastric bypass surgery are at risk.
Obese individuals who have undergone gastric bypass surgery may become vitamin D deficient over time without a sufficient intake of this nutrient from food or supplements, since part of the upper small intestine where vitamin D is absorbed is bypassed and vitamin D mobilized into the serum from fat stores may not compensate over time.
Laboratory and animal evidence as well as epidemiological data suggest that vitamin D status could affect cancer risk. Strong biological and mechanistic bases indicate that vitamin D plays a role in the prevention of colon, prostate, and breast cancers. Emerging epidemiological data suggest that vitamin D may have a protective effect against colon cancer.
How much Vitamin D do we need?
The most comprehensive survey ever undertaken on vitamin D in Canadians has found widespread deficiencies of the sunshine vitamin, which is being promoted for everything from the prevention of cancer to reducing heart attack risk.
The survey, conducted by Statistics Canada, found that two-thirds of the population has vitamin D levels below the amounts associated with reduced risk of chronic diseases such as cancer. One in 10 people, have such low readings that they don’t have enough for good bone health. About 4 per cent have so little that they’re at risk for rickets, a debilitating childhood bone disease.
The The survey also found a huge vitamin D disparity among Canadians based on racial origin, with whites having substantially higher concentrations than the prevailing levels in the country’s growing non-white population. Whites had an average of nearly 40 per cent more of the nutrient than non-whites.
It termed low levels of the vitamin a “worldwide problem,” and said most Canadians don’t have concentrations at “the level proposed for optimal health.”
It said some of the biggest factors in low vitamin D readings were being non-white and consuming a smaller amount of milk, which is fortified with the vitamin.
Gerry Schwalfenberg, an assistant clinical professor in the department of family medicine at the University of Alberta, said testing showing that “60 to 70 per cent [of Canadians] have inadequate levels, not good,” given that vitamin D insufficiency is being linked to so many chronic diseases.
Health Canada, in conjunction with U.S. government agencies, set a recommended daily intake in 1997 based on the relatively low amounts needed for good bone development. The new data indicate that a substantial number of Canadians aren’t getting enough even for this purpose, let alone the far higher levels suggested for the prevention of chronic diseases.
Reinhold Vieth, professor of nutrition at the University of Toronto, said people with readings below 50 nmol/L may have so little of the nutrient that their bodies will scavenge calcium from bones to meet other metabolic needs.
Vitamin D is needed to properly absorb calcium and phosphorous, but nearly every cell has receptors for it, and it is involved in the proper functioning of hundreds of genes.
Statistics Canada tested the vitamin D in blood from about 5,300 people aged 6 to 79, a sample group it said was representative of the vast majority of Canadians. About half of 1 per cent had readings over 220 nmol/L, indicating high sun exposure, high use of supplements or tanning lights. No one had levels above the 375 nmol/L considered potentially toxic.
Health Canada says Canadians should take from 200 to 600 International Units of vitamin D a day for good bone health. A cup of fortified milk contains about 100 I.U., while a typical multivitamin has 400. But some researchers say this amount is woefully inadequate. Dr. Schwalfenberg says vitamin D’s anti-cancer benefit “probably begins at 90 nmol/L. That would require at least 3,000 I.U. a day to achieve.”