There’s a joke you may have heard about shedding winter pounds in the summer time. It’s almost as if some vestige of hibernation still exists in people and we begin to pack on the pounds in preparation for a long winter with little food and even less warmth. We then have to shed the weight once the weather improves.


With recent interest in the relation between vitamin D and obesity, there could be something to the idea of increasing winter body weight. As most of us know, we get vitamin D both in our diet and by exposure to sunlight. More intense and longer duration of summer rays increase our vitamin D levels, and just might be a signal to our bodies to drop some weight. In a recent review in the Nutrition Journal, researchers took an in-depth look at the role vitamin D plays in the body, with a focus on how it affects body fat.


First, the researchers looked at genetic factors. Vitamin D interacts with fat tissue through a few mechanisms. First, it increases gene expression of immune-modulatory and anti-proliferative effects, meaning that it helps to boost the immune system and prevents the growth of unwanted substances.


Vitamin D also impacts body fat through other mechanisms that are not genetic. These include increased protein expression and benefits to oxidative stress, inflammation, and cellular metabolism. All of these indirect routes would also be related to the reduction of body fat.


So, due to its benefits to the body both through genetic and non-genetic factors, vitamin D should also improve body fat composition. However, the issue gets a little cloudy at this point. Vitamin D does seem to help prevent metabolic syndromes that lead to diseases like diabetes, and vitamin D deficiency is a risk factor for increased body fat. But prevention seems to be where it ends.


For those who are already obese, the results are less stellar. Despite benefits to genetic and non-genetic factors, vitamin D supplementation doesn’t seem to help reduce body fat. In fact, in obese patients, vitamin D doesn’t even seem to have the same benefits as it does in people with less body fat. Since vitamin D is fat-soluble and frequently stored in fat tissue itself, it’s possible that its effects are muted by heightened rates of absorption when there is excess body fat. In fact, "stored” might not even be the right word here. "Held hostage" might be more like it.


While vitamin D shows copious benefits to health and the maintenance of a healthy bodyweight in already healthy people, it doesn’t seem to reduce existing obesity. However, there is some promise in a metabolite of vitamin D, called calcitriol. More research is needed to study calcitriol, but until then, traditional dietary interventions for obesity such as reducing the intake of unhealthy foods will have to do.



1. Khanh vinh quốc Lương,, “The beneficial role of vitamin D in obesity: possible genetic and cell signaling mechanisms,” Nutrition Journal 2013, 12:89


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