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Health Benefits
of vitamin D
Vitamin
D has often been taken for granted. Most of us are only familiar
with this vitamin's major job, which is to help maintain the body's
calcium balance by increasing calcium absorption. But this hormone-like
vitamin plays a crucial role in many metabolic processes, and
may have subtle but important effects on regulating cell growth
and on our immune and cardiovascular systems (1). A strong connection
has recently been found, for example, between low blood levels
of vitamin
D and congestive heart failure-a condition which afflicts
many seniors (2). And an emerging link between vitamin
D and some cancers is an area of active investigation. When
it comes to bone health, however, calcium usually gets all the
attention. Now, new research suggests that even an abundance of
calcium won't keep the skeleton strong if vitamin
D is lacking.
Vitamin
D: A Key to Reducing Bone Fractures
Short term trials of calcium supplementation show that it slows the loss of bone density in older women, yet longer term observational studies have not generally found that higher calcium diets actually reduce the risk of disabling hip fractures. That led Harvard researchers to focus on vitamin D in over 70,000 postmenopausal women followed for 18 years. Women consuming at least 500 IU of vitamin D from food and supplements had a 37% lower risk of hip fracture than those who got less than 140 IU daily (3). Overall, total calcium intake did not appear to be associated with a lower risk of hip fracture, suggesting that low D has a great impact on calcium absorption and bone health even when calcium intake is sufficient. These findings are consistent with those from another study published this month, reporting that vitamin D supplements reduced hip fracture incidence in older men and women (4).
Too Little
Vitamin D Is Common
Vitamin
D experts like Dr. Michael Holick of Boston University are
concerned that vitamin
D deficiency is becoming a major public health problem. Deficiency
is known to be common in older people, but government surveys
have also identified low blood levels in many younger women, particularly
African-American women (5). People who spend most of their time
indoors or who live in Northern places, are at risk as well. Dr.
Holick and his team found that 36% of young medical students and
hospital residents-people who work long hours and rarely see the
light of day-were vitamin
D insufficient at the end of winter.
How to
Get More Vitamin D
Sunlight creates vitamin
D in the skin. If you get enough sun exposure in the spring-fall
seasons, you'll have some stores to help carry you through the
winter months. The problem is that winter sunlight is too weak
for vitamin
D production in much of the northern portion of the US. And
many people don't get outdoors regularly, or wear sunscreen when
they do. Dr. Holick suggests waiting 5-15 minutes before applying
sunscreen when outside, several times weekly. People with darker
skin may need more time than those with lighter pigmentation.
A few foods contain vitamin
D-mackerel, salmon and sardines are about the highest. Fortified
milk contributes some D,
but older people would have to drink six to eight glasses daily
to achieve recommended intakes from milk alone. Dr. Holick recommends
an additional daily multivitamin that contains vitamin
D.
References
- Holick MF. Vitamin
D: A millennium perspective. J Cell Biochem 88:296-307,
2003.
- Zittermann A et al. Low vitamin D status: a contributing factor in the pathogenesis of congestive heart failure. J Am Coll Cardiol 4:105-12, 2003
- Feskanich D et al. Calcium, vitamin D, milk consumption and hip fractures: a prospective study among postmenopausal women. Am J Clin Nutrition 77:504-11, 2003.
- Trivedi D et al. Effect of four monthly oral vitamin D3 supplementation on fractures and mortality in men and women living in the community.British Med J 326:469-72, 2003
- Nesby-O'Dell S et al. Hypovitaminosis D prevalence and determinants among African American and white women of reproductive age: Third National Health and Nutrition Survey. Am J Clin Nutr 76:187-92, 2002.
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