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Weight loss in the obese boosts vitamin D levels

American Journal of Clinical Nutrition,
May 2011
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Weight loss in the obese boosts vitamin D levels

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Older women who are overweight or obese and lose more than 15 percent of their body weight could significantly boost their levels of vitamin D.

Since vitamin D is generally lower in persons with obesity, it is possible that low vitamin D could account, in part, for the link between obesity and diseases such as cancer, heart disease and diabetes. The study, conducted in Seattle, America indicates that the surge in vitamin D could help scientists explore new avenues for the prevention of these chronic diseases.

Vitamin D is fat-soluble nutrient that plays many important roles in the body, including promoting calcium absorption and is needed for bone growth and bone healing. Along with calcium, vitamin D helps protect older adults from osteoporosis. The nutrient also influences cell growth, neuromuscular and immune function, and reduces inflammation. Many gene-encoding proteins that regulate cell proliferation, differentiation, and apoptosis (programmed cell death) are modulated in part by the vitamin.

It's found in certain foods, such as fatty fish, and produced naturally in the body through exposure of skin to sunlight. Just 10 minutes of sun a day is enough to trigger adequate vitamin D production. The estimated average requirement via diet or supplementation is 400 international units per day for most adults. The optimal blood level of vitamin D is thought to be between 20 and 50 ng/mL, Levels under 20 ng/mL are inadequate for bone health and levels over 50 ng/mL are associated with potential adverse effects, such as an increased risk of developing kidney stones.

Researchers conducted a year-long study to assess the effect of weight loss on vitamin D. They assigned 439 overweight or obese postmenopausal women to one of four regimens: exercise only, diet only, exercise plus diet and no intervention. About 70 percent of the participants had less-than-optimal levels of vitamin D when the study began; at baseline, the mean blood level of vitamin D among the study participants was 22.5 ng/mL. In addition, 12 percent of the women were at risk of vitamin D deficiency (blood levels of less than 12 ng/mL).

Women who lost up to 10 percent of their body weight (10 to 20 pounds) through diet and exercise saw modest increases in vitamin D, those levels were roughly three times higher in women who dropped more than 15 percent of their body weight, regardless of dietary intake of the nutrient.

The researchers were surprised at the effect of weight loss greater than 15 percent on blood vitamin D levels. It appears that the relationship between weight loss and blood vitamin D is not linear but goes up dramatically with more weight loss. It is thought that obese and overweight people have lower levels of vitamin D because the nutrient is stored in fat deposits. During weight loss, it is suspected that the vitamin D that is trapped in the fat tissue is released into the blood and available for use throughout the body.

The findings suggest the greater the weight loss, the more meaningful the surge in vitamin D levels. However, the researchers noted that the degree to which vitamin D is available to the body during and after weight loss remains unclear. They also cautioned that more targeted research is needed to understand any link between vitamin D deficiency and chronic disease.

Monday, 13 June 2011


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