Travis’ Note: Today’s guest post comes from our friend and colleague Dr Caitlin Mason. More details on Caitlin and her work can be found at the bottom of this post.
In most places, the arrival of summer brings with it more opportunities to be outside, fewer clothes and more vitamin D. And, vitamin D is a hot topic these days.
It has long been known that vitamin D is important for bone health, but vitamin D receptors are found in more than 30 cell types & it has diverse non-skeletal roles as well. Some, albeit certainly not conclusive, evidence suggests it could have a protective role against heart disease, cancer, and a variety of autoimmune diseases.
Blood vitamin D concentrations are consistently lower in persons with obesity and it has been hypothesized that these low levels could be one factor that helps account for increased risk of heart disease, cancer, and other chronic conditions associated with overweight and obesity.
The prevailing hypothesis is that vitamin D (a fat-soluble compound) is taken up and stored in the body’s fat depots, making it physiologically unavailable to circulate in blood and be transformed via the liver and kidneys into its biologically active form.
If true, then weight loss could theoretically increase the amount of vitamin D circulating in the blood. But, whether this occurs and how much weight loss actually affects blood levels of vitamin D has not been widely examined.
Thus, as part of a team of researchers that is interested in how obesity influences breast cancer risk, we recently conducted a study to measure the impact of weight loss on blood levels of vitamin D. If interested, the full paper was recently published in the American Journal of Clinical Nutrition.
What did we find?…in short , that losing 5-15% of body weight through diet and/or exercise (an amount that is usually accompanied by fairly significant metabolic improvements ) only raised blood vitamin D levels by a very modest 2-3 ng/mL, an amount equivalent to what could be expected from taking a standard multivitamin. However, the rise in blood concentrations was much greater (more than double) in women who lost more than 15% of their starting weight. This seems to indicate that the body doesn’t ‘release’ vitamin D into the bloodstream in an amount that is directly proportional to weight loss; rather, there may be a threshold effect . And, understanding this threshold may lead to a clearer understanding of how reduced body weight influences disease risk.
The implications for this are probably more important to helping understand vitamin D metabolism than they are for weight loss recommendations or for guiding nutritional intake. Vitamin D metabolism in the body is a particularly complex process and currently the ‘optimal’ level of blood vitamin D for maintaining health is hotly debated.
Sadly, most nutritional research seems to become considerably less useful by our propensity to focus on single nutrients rather than more holistic dietary and behaviour patterns (Read more about Dr. David Katz’s take on the ONAAT (One Nutrient At A Time) fallacy here. You probably remember when Vitamin E was thought to be the answer to all our woes, or fiber? Anti-oxidants?
Understanding the interrelationships between vitamin D, obesity, and disease risk certainly could uncover new avenues for disease prevention, but I’m betting it’s not a panacea.
So, until we have a better understanding of how vitamin D influences body fat and disease risk, I personally take a multivitamin, a little extra vitamin D in the winter, wear sunscreen, & try to get outside for at least half an hour of daylight exercise every day.
Caitlin Mason is a postdoctoral fellow at the Fred Hutchinson Cancer Research Center in Seattle, Washington. Her research focuses primarily on understanding the relationships between physical activity, obesity, and cancer risk, including breast cancer.
Caitlin Mason, Liren Xiao, Ikuyo Imayama, & et al. (2011). Effects of weight loss on serum vitamin D in postmenopausal women American Journal of Clinical Nutrition : ajcn.111.015552v194/1/95
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