Investigators at the Kaiser Permanente Center for Health Research followed over 4,600 women, aged 65 and over, for close to 5 years, and found that women with the lowest levels of 25-(OH)-vitamin D gained on average two more pounds than those with normal serum levels of the vitamin.
Over the 4.5-year period, 12% of the women gained 5% or more of their baseline body weight, and 78% of these women were vitamin D-deficient. Among the 27% of women who lost 5% or more of their baseline weight over the course of the study, there seemed to be no correlation with vitamin D status (Leblanc ES, et al, J Womens Health. 2012 Jun 25. [Epub ahead of print])
The Kaiser researchers also noted that women with 25(OH)D levels equal to or greater than 30 ng/mL had significantly lower baseline weights (141.6 lb) compared to women with levels less 30 ng/mL (148.6 pounds).
Endocrinologist and lead author, Erin LeBlanc, MD, said that this was one of the first studies to show that low levels of vitamin D predispose women to weight gain. It's an important finding because many epidemiological studies show that a vast majority of Americans, especially elderly people, do not get adequate dietary vitamin D, and rarely get enough from sun exposure.
These findings add further support to the notion that vitamin D is a quasi-hormone with multiple and far-reaching metabolic effects.
From the perspective of evolutionary biology, the observation that low vitamin D fosters weight gain makes good sense. Among our ancient ancestors, sun exposure was the primary source of vitamin D, and levels tended to be higher during the summer when people spent more time outside, and lower during the cold winter months.
Physiologically, a low level of the so-called "sunshine" vitamin may be a signal for the body to shift into a wintertime metabolic pattern, characterized by fat storage and weight gain.
Whether supplementation with vitamin D can, in and of itself, promote weight loss is another question, and one that requires much more research. Dr. LeBlanc hesitated to draw any such conclusions from the findings of her study.
Another important, unanswered question is whether the weight-promoting effect seen in this population of post-menopausal women could be generalized to younger women, or to men of any age.
Data from a study of pregnant women in the UK suggest that maternal vitamin D status can affect childrens' propensity toward weight gain.
Investigators at the Medical Research Council Lifecourse Epidemiology Unit, Southampton General Hospital, measured vitamin D in 977 women at 34 weeks' gestation, and then tracked lean and fat mass among their babies at 3 weeks, 4 years and 6 years of age.
They found that low vitamin D status during pregnancy did not seem to affect a child's fat mass at birth, but it strongly affected fat mass at ages 4 and 6; children born to women with intrapartum vitamin D levels below 50 ng/ml showed substantially higher fat mass than those born to women with higher vitamin D during pregnancy (Crozier SR, et al. Am J Clin Nutr. 2012 Jul;96(1):57-63. Epub 2012 May 23.)
The Southamton researchers stressed that the inverse correlations were robust, even after correcting for a range of potentially confounding variables like maternal BMI and weight gain during pregnancy. They view their findings as adding to "a growing evidence base for a role of vitamin D in the origins of adiposity."