Vitamin D is a vitamin with hormone-like properties. Its primary purpose is to increase calcium absorption from the gut and the kidneys to help get calcium into the bones. Researchers were hopeful that boosting vitamin D status might protect against osteoporosis and the fractures that go along with it. However, recent studies looking at whether vitamin D prevents bone fractures have been disappointing.
Unfortunately, the preponderance of studies show that taking vitamin D supplements, if you’re not deficient, doesn’t prevent bone fractures related to osteoporosis. However, vitamin D has other potential health benefits. For example, this hormone-like vitamin plays a role in immune function. Some studies suggest a higher level of vitamin D may reduce the risk of some autoimmune conditions, especially multiple sclerosis.
We do know that vitamin D deficiency is common. In a large study called the National Health and Nutrition Examination Survey, 41.6% of adults tested had a vitamin D level below 20 ng/ml, the minimum recommended for bone health. Risk factors that increase the likelihood of vitamin D deficiency include:
· Living at a Northern latitude
· Being over the age of 60
· Dark skin type
· Limited sun exposure
· Being institutionalized or hospitalized
· Certain medications
· Certain health conditions that reduce absorption of vitamin D, such as inflammatory bowel disease
· Being obese
It’s clear that we don’t want to be deficient in vitamin D and a significant portion of the population is. It’s not surprising since the population is aging and becoming more overweight and obese. Both are risk factors for vitamin D deficiency.
You might wonder how obesity increases the risk of vitamin D deficiency. Vitamin D is stored inside fat tissue. People who are overweight or obese have a harder time mobilizing stored vitamin D. The vitamin D is “stuck” inside the fat tissue and can’t be released so that the body can use it. Vitamin D is pretty useless inside of fat cells and tissues. So, overweight and obese people can be deficient in vitamin D in the midst of plenty. It’s like having your cabinets packed full of food and being unable to open them to get it out.
Research shows obese people, in general, have lowering circulating levels of vitamin D than leaner folks. In fact, research shows that vitamin D levels drop by 4.2% with every 10% increase in body mass index. Even when you give a person with lots of fat tissue a supplement, their blood levels of vitamin D rise more slowly because it gets sequestered into fat tissue.
How Exercise May Improve Vitamin D Status in Obese People
Exercise has a long list of health benefits, but can it help with vitamin D status too? That’s what researchers are exploring. What happens when you’re physically active? You mobilize fat from fat stores. Researchers now think that vitamin D stored in fat tissue is released in response to exercise too. As the fat is mobilized from stored fat tissue, so is the vitamin D.
In fact, studies show a link between high levels of physical activity and higher vitamin D status. You might assume that people who are more physically active spend more time outside and that could explain their better vitamin D status. They’re getting more sun exposure! We have compounds on our skin that the sun converts to vitamin D precursors that are further activated by the body.
However, a study showed that humans who cycled on a bike for 30 minutes experienced a bump-up in vitamin D level right after a workout. The benefits were immediate. This makes sense if vitamin D is being mobilized from fat tissue during exercise.
So, obese people have a harder time mobilizing fat during a workout. However, regular physical activity makes mobilizing fat as fuel easier and, along with it, stored vitamin D. In fact, obese people who exercise regularly have an easier time releasing fat stores in other situations such as during fasting. So, exercise may have another perk for people who are obese. Regular workouts may increase their ability to mobilize fat stores and the vitamin D stored in that fat.
What You Should Know about Vitamin D
We still don’t know enough about the effects of vitamin D on tissues other than bone. The evidence that taking vitamin D supplements when you aren’t deficient to protect against osteoporosis, bone fractures, or falls is weak. However, it is important to not be deficient, as that can negatively impact bone health and, potentially other aspects of health, such as immune function. Some studies suggest vitamin D may protect against certain forms of cancer and heart disease and reduce inflammation as well. However, there isn’t strong evidence that taking supplemental vitamin D protects against these conditions. Still, a lot of factors conspire against an individual getting enough vitamin D. Most foods, with the exception of eggs, fatty fish, and mushrooms exposed to ultraviolet light, aren’t good sources of vitamin D. The best source is sunlight exposure. Many people spend too much time indoors and live in areas where they don’t get a lot of direct sunlight. A recent study even found that environmental pollution makes it harder to maintain a sufficient vitamin D level. Although most health care professionals don’t routinely test vitamin D levels, it’s a good idea to know your level, especially if you are at higher risk for deficiency.
The Bottom Line
More vitamin D isn’t better but not enough is harmful. As far as the other potential health benefits of vitamin D, we need more research. But it’s possible that when you contract your muscles through exercise and mobilize fat stores, you’re giving your body greater access to stored vitamin D. So, take advantage of it!
References:
· Environ Int. 2019 Jan;122:67-90. doi: 10.1016/j.envint.2018.11.052
· Nutr Res. 2011;31(1):48.
· Mobilizing vitamin D from adipose tissue: The potential impact of exercise. A. Hengist O. Perkin J. T. Gonzalez J. A. Betts M. Hewison K. N. Manobpoubs K. S. Jones A. Koulman. 03 February 2019
· U.S. Preventive Services Task Force. “Evidence Summary Other Supporting Document for Vitamin D Deficiency: Screening”
· Science-Based Medicine. “Do vitamins prevent cancer and heart disease?”
· Live Science. “Obesity Is Linked to Vitamin D Deficiency”
Short Summary:
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