The Skinny on Vitamin D, the Sun, and Weight Loss

6 years ago

With daylight savings time bringing more sunshine into our day (thank goodness!) it reminds me of a question I was recently asked about whether vitamin D can help with weight loss.   Lots of hoo-ha about Vitamin D lately.   Vitamins seem to be taking their turns in the spotlight, eh?   First there was Vitamin C, kicking everything from scurvy to the common cold, even if the latter is more based on wishful thinking than scientific evidence… but hey, look at the market for Vitamin C-laced cough drops, cold-kicking concoctions, and even candy!  (insert cash register noise)  Then Vitamin A’s cousin Lycopene, found in tomatoes and strawberries, stole the show temporarily with studies revealing its association with reduced risk for cancer and heart disease.  Even ketchup companies slapped the LYCOPENE! sticker on their bottles to make us temporarily forget about the high fructose corn syrup and salt.  Ketchup to reduce heart attacks?   Nice try, Heinz.  But now Vitamin D is taking the lead in the vitamin race.  Vitamin D is often referred to as the “sunshine” vitamin because one form of vitamin D (D3) is made in the skin via a reaction that occurs with exposure to sunlight (AKA, ultraviolet radiation, UVR).  Vitamin D can also be found in fortified dairy products (milk, yogurt), dietary supplements, as well as naturally in fatty fish (salmon, tuna) and eggs.  Vitamin D is necessary for the body to absorb calcium (which is why milk is always fortified with it), and integral to bone health.  Lately though, much ado has been going on about vitamin D’s impact on almost every aspect of human health, including obesity.  Vitamin D “champion” Dr. Michael Holick out of Boston University heads up the hype on vitamin D with his best-selling book, The Vitamin D Solution which purports that Vitamin D “is absolutely needed to prevent and treat our chronic disease epidemic including heart disease, cancer, diabetes, depression, obesity, and autoimmune disease” per a blurb on his website. Of course, as an obesity expert, I am intrigued by the claims regarding the treatment of obesity. Let’s look further into the research on this topic….

The hype began when several observational studies reported an association between vitamin D deficiency and obesity, such that heavier people have lower levels of vitamin D in their blood.  One reason for this is that vitamin D is fat soluble. The more body fat that you have the more that vitamin D will be dissolved and stored in fat rather than available in blood.  This doesn’t mean that people with more fat have LESS vitamin D, just that their blood has less vitamin D.  Whether vitamin D stored in fat is less “active” is still up for debate.  (Please see Reddy and Gilchrest 2010).

Let’s assume for the sake of argument that vitamin D stored in fat is less “active” than vitamin D in the blood and that the “deficiency” found in people with higher body weights is real.  Does this mean that vitamin D supplementation (via food, supplements or the sun) will help REDUCE body weight?

I reviewed the literature going back 10 years and found only 2 trials that have directly tested this question.  In one of the trials by Zitterman and colleagues (2007), people in a weight loss program were randomized to placebo or vitamin D supplement (83 microgm/dl) and followed for a year.  The vitamin D group did not lose more weight than the placebo group, but they did have greater decreases in triglycerides, which is good news.  The bad news is that their LDL-C (“bad”) cholesterol (a risk factor for heart disease) significant INCREASED compared to the placebo group.  Hmmm….  A second study by Major and colleagues (2009) randomized people in a 14-week weight loss program to a supplement containing calcium plus vitamin D or a placebo and found no differences in weight loss between groups.  They did find an advantage in the calcium/vitamin D group on HDL (good cholesterol) and HDL:LDL ratio, which is good news.  With only 2 studies and both showing no impact on weight, where is the hype that vitamin D helps with weight loss coming from???   Well, there are a few studies that show that the amount of weight someone loses in a weight loss program is associated with increases in serum vitamin D.  (See Shahir and Miller studies below)  I do not interpret these findings as vitamin D causing the weight loss but rather possibly that as people are reducing their weight (fat mass), their serum vitamin D rises (less fat for the vitamin D to get absorbed into) OR that healthier diet is what is causing the weight loss and vitamin D along with other nutrients increase in people who improve their diets.

The bottom line is that I see NO compelling evidence that increasing your vitamin D will at all help you to lose weight.  Vitamin D does appear to be essential to bone health and if you are at all at risk for osteoporosis, you should speak to your physician about identifying and correcting a deficiency.

Let’s go back to the issue of the sun.  Should we be tanning to lose weight?  The 2 studies I mentioned above tested the effects of vitamin D dietary supplements on weight.  Dr. Holick, vitamin D champion, suggests that much larger amounts of vitamin D can be had from sun exposure.  He recommends direct sun exposure on legs and arms 5-10 minutes three times a week at midday in the spring and summer and use of artificial sources (tanning booths) in the winter when UVR from the sun is not strong enough or available enough to generate adequate vitamin D (  His recommendations are an object of much debate given that UVR is a known carcinogen (definition:  cancer causing agent), and overexposure is associated with melanoma (skin cancer).  In fact, UVR (let me remind you that “R” stands for “radiation”) from tanning booths has been assigned the status of Class 1 carcinogen by the International Agency for Research on Cancer. Other Class 1 carcinogens include arsenic, radon, and mustard gas.  I personally will be no more likely to use a tanning booth for weight control than I would to use sweet-tasting arsenic as a sugar substitute in my coffee. I should also note that Dr. Holick receives funds for his research from the UV Foundation which is sponsored by….wait for it…. the Indoor Tanning Association.

Rats!  Now my summer plans of laying in the sun, eating ketchup by the spoonful, and popping vitamin C candies in the name of health are spoiled!

I guess at the end of every search for new weight loss solutions, we always end up in the same place... healthy diet and physically active lifestyle...



Lagunova Z, Porojnicu AC, Lindberg FA, Aksnes L, Moan J. Vitamin D status in Norwegian children and adolescents with excess body weight. Pediatr Diabetes. 2011 Mar;12(2):120-6.

Reddy KK, Gilchrest BA. J Invest Dermatol. 2010 Feb;130(2):321-6. What is all this commotion about vitamin D?

Zittermann, A., Frisch, S., Berthold, HK, Gotting, C., Kuhn, J., Kleesiek, K., Stehle, P., Koertke, H., Koerfer, R. Vitamin D supplementation enhances the beneficial effects of weight loss on cardiovascular disease risk markers. American J of Clin Nut, 2009, 89(5); 1321-7.

Shahar DR, Schwarzfuchs D, Fraser D, Vardi H, Thiery J, Fiedler GM, Blüher M, Stumvoll M, Stampfer MJ, Shai I; DIRECT Group. Dairy calcium intake, serum vitamin D, and successful weight loss. Am J Clin Nutr. 2010 Nov;92(5):1017-22.

Major, GC, Alarie, F, Dore, J., Phouttama, S, Tremblay, A. Supplementation with calcium + vitamin D enhances the beneficial effect of weight loss on plasma lipid and lipoprotein concentrations. Am J Clin Nutr. 2007 Jan;85(1):54-9.

Miller, GD. Improved nutrient intake in older obese adults undergoing a structured diet and exercise intentional weight loss program. J Nutr Health Aging. 2010 Jun;14(6):461-6.

El Ghissassi F, Baan R, Straif K, Grosse Y, Secretan B, Bouvard V, et al. A review of human carcinogens--part D: Radiation. Lancet Oncol 2009;10(8):751-752.

International Agency for Research on Cancer Working Group. The association of use of sunbeds with cutaneous malignant melanoma and other skin cancers: A systematic review. Int J Cancer 2006;120(5):1116-1222.

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