New research about the link between vitamin D and metabolism

By Cynthia Sass
June 28, 2012

There has been a lot of news about weight control recently, from the new FDA-approved weight loss drug to research supporting the notion that, not all calories are created equal, something I've blogged about in previous posts. But what has really caught my eye is new research about the link between vitamin D and weight control. A National Institutes of Health (NIH) study, published in the Journal of Women's Health, looked at more than 4,600 older women and found that over a five year period, those with low blood levels of Vitamin D gained about two pounds more than those with adequate levels. Two pounds may not sound like much, but a two pound gain every five years can really add up, and contribute to an increased risk for several health problems, including heart disease, diabetes, and cancer. This isn't the first research to link vitamin D to weight control, and several studies have revealed that most of us aren't getting enough. In the NIH data, nearly 80 percent of women had insufficient levels of Vitamin D. That doesn't surprise me, because even after taking a daily supplement of 400 IUs for many months my own blood vitamin D level was too low.

Vitamin D earned the nickname the "sunshine vitamin" because exposure to the sun's ultraviolet rays triggers its production in the body. But studies seem to indicate that you can't rely on the sun as your sole source. Where you live, the season, time of day, cloud cover, smog, and sunscreen all affect UV exposure and vitamin D production. One recent study found that 51 percent of sun-drenched Hawaiians, who spend over 20 hours per week outdoors without sunscreen, still had low levels of vitamin D.

The only way to know your status is to have a 25-hydroxyvitamin D test, which measures the level in your blood. Some doctors now routinely add this test to check-ups but you may need to request it. I highly recommend it because the results will indicate if you need a supplement and, if so, the proper dose. While many physicans and reseasrchers believe that 400 IU, 100 percent of the daily value, is not enough, which was true in my case, getting too much may also be risky. Excess supplemental vitamin D has been linked to high blood calcium levels, which can cause kidney and heart damage. As for food sources there are only a few natural, unprocessed foods that provide vitamin D, including salmon, mackerel, whole eggs, and mushrooms. Striking the right balance between foods and supplements combined-not too little, not too much is the key to reaping the rewards and avoiding the risks.

It's worth getting tested. A recent eight year study revealed that adults with the lowest blood levels of vitamin D were about twice as likely to die from any cause compared to those with the highest levels. Other research has linked adequate vitamin D to lower rates of obesity, type 2 diabetes, heart disease, high blood pressure, osteoporosis, and certain cancers. And as for weight control, another recent study from the University of Minnesota tested blood vitamin D levels in 38 overweight men and women before and after they followed a diet plan for 11 weeks that slashed 750 calories a day. All the subjects were found to have low levels but for every increase of one nanogram per milliliter of blood vitamin D status, the dieters lost an extra half a pound. Higher baseline vitamin D levels were also tied to a greater loss of belly fat. Pretty potent stuff!

Have you had your blood vitamin D level tested? Did you know that sun exposure may not be be enough? Please tweet your thoughts to @cynthiasass and @Shape_Magazine.


Cynthia Sass is a registered dietitian with master's degrees in both nutrition science and public health. Frequently seen on national TV, she's a SHAPE contributing editor and nutrition consultant to the New York Rangers and Tampa Bay Rays. Her latest New York Times best seller is S.A.S.S! Yourself Slim: Conquer Cravings, Drop Pounds and Lose Inches.