[PHNUTR-L] Vitamin D in Elderly Said to Sequester Itself in Fatty
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Mon Jun 11 08:20:26 PDT 2007
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Vitamin D in Elderly Said to Sequester Itself in Fatty Tissue
By Michael Smith, Senior Staff Writer, MedPage Today
Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University of
Pennsylvania School of Medicine.
June 08, 2007
BOSTON, June 8 -- As elderly patients get fatter, their blood levels of
vitamin D decline even if they continue to go out into the noonday sun,
according to researchers here.
* Explain to interested patients that vitamin D plays several key
roles in human health, including keep bones strong.
* Explain that Vitamin D levels drop as elderly patients put on
weight, although the reason for the decline has not been clear.
* Explain that the study appears to rule out the idea that the
vitamin D decline in older patients who gain weight can be attributed to
the explanation that they tend to stay indoors, away from the sun.
Instead, the most likely explanation is that the fatty tissue sequesters
vitamin D and stops it from getting into the circulation, found Susan
Harris, D.Sc., of the Jean Mayer USDA Human Nutrition Research Center on
Aging at Tufts University here.
The finding comes from a cross-sectional examination of baseline data
from 381 volunteers talking part in a three-year trial of calcium and
vitamin D supplementation to reduce bone loss in men and women 65 and
older, Dr. Harris and co-author Bess Dawson-Hughes, M.D., also of Tufts,
reported online in the Journal of Clinical Endocrinology & Metabolism.
Patients 65 and older with high body fat have lower levels of
25-hydroxyvitamin D, the storage form of vitamin D, compared with those
who have lower body fat, Dr. Harris said.
There are several competing explanations, she said, but the two most
* The fatter the patients, the more likely they are to stay indoors
and not get enough sunlight to synthesize vitamin D.
* The fatty tissue keeps vitamin D from entering the bloodstream.
To seek the more likely explanation, the researcher stratified the
volunteers into quartiles, according to percentage of body fat, with the
lowest being below 27.5% and the highest 40.3% or higher.
Volunteers in the study had not yet taken any vitamin D supplements and
were excluded if they had recently traveled south of latitude 35 or were
not Caucasian (because there is evidence that the link between body fat
and vitamin D varies according to race).
Dietary vitamin D and sun exposure was estimated using a questionnaire
and body fat was measured by dual-energy x-ray absorptiometry, the
* There was a significant inverse correlation (at P=0.003) of fat
percentage with vitamin D intake.
* Circulating levels of 25-hydroxyvitamin D were about 20% lower in
the highest quartile compared with the lowest -- 26.7 ng/mL, compared
with 33.2. The difference was significant at P=0.03.
* Few of the volunteers reported sunscreen use (10% of men and 21%
of women) and it did not vary across fat quartiles.
* Men spent significantly more time outside than women (at P<0.001)
and both sexes spent significantly more time outside from May to October
than from December to April (also at P<0.001).
* The time spent outside did not vary significantly across
quartiles of body fat.
* In contrast to 25-hydroxyvitamin D, the concentration of 1,25
(OH)2D did not differ across quartiles (P=0.654).
"Sunlight exposure could not account for low vitamin D stores in older
people with high percent body fat," Dr. Harris said.
The finding is important because vitamin D plays an important role in
bone health, according to Dr. Dawson-Hughes. "There is evidence that
many older Americans have low blood levels of vitamin D, which can put
them at risk for bone fractures and osteoporosis," she said.
The finding also comes as researchers are reporting that high vitamin D
levels can cut the risk of cancer in women by up to 60%.
The researchers noted that the results can't be extrapolated widely.
"These results cannot be carried over to other populations, such as
young people, or elderly living in different climates," Dr. Harris said.
But if low vitamin D stores aren't a result of low sun exposure in this
population, she added, "it suggests that we should explore other
The study was supported by the U.S. Department of Agriculture and the
National Institutes of Health. The authors said they had no conflicts to
Additional source: Journal of Clinical Endocrinology & Metabolism
Harris SS et al. "Reduced Sun Exposure Does Not Explain the Inverse
Association of 25-Hydroxyvitamin D with Percent Body Fat in Older
Adults." J Clin Endocrin Metab 2007;
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
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