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What has sunlight got to do with diabetes?

What has sunlight got to do with diabetes?

People with vitamin D deficiency have a lower insulin secretion than those with optimal levels of the vitamin, according to some studies
People with Vitamin D deficiency are at high risk of developing Type 2 diabetes
Photo by Anantha Subramanyam K/Happiest Health

Over the years, increased urbanisation and modern lifestyles have meant most people don’t get enough sunlight exposure in their day-to-day life. And the trend shows no sign of slowing — in fact, it got a boost during the Covid-19 pandemic.

This lack of sunlight means an increase in cases of vitamin D deficiency. Experts also say that the sunlight entering rooms through windows is not sufficient since the ultraviolet rays get filtered by glass.

Some studies have even linked vitamin D deficiency to type 2 diabetes. One study published recently in the Cureus Journal of Medical Science states that people with vitamin D deficiency had 48% lower insulin secretion than those with optimal levels of the vitamin.

Vitamin D deficiency and diabetes

Dr Sonali Kagne, deputy consultant, department of endocrinology, Sir HN Reliance Foundation Hospital, Mumbai, says though many studies have shown lower vitamin D levels in people with obesity and type 2 diabetes, it is still unknown if vitamin D deficiency can cause type 2 diabetes. The possible mechanism by which vitamin D deficiency can lead to diabetes is by predisposing the body to the development of insulin resistance, she adds.

“Tissues require higher amounts of insulin for glucose utilisation. The beta cells can overcome this resistance by releasing more insulin, thus preventing high blood glucose levels. However, as this hyperactivity increases, they experience excessive oxidative stress, resulting in beta cell death and the onset of diabetes,” she says, adding that vitamin D can help reduce the oxidative stress, which in turn can help prevent diabetes.

Vitamin D also acts to reduce inflammation — and hence, insulin resistance.

Diabetologist and endocrinologist Dr Anjali Bhatt says there is no direct cause-and-effect relationship between vitamin D deficiency and diabetes. The association between the two conditions is usually found also because they are very common problems and can hence present together, says Dr Bhatt, also founder and chief consultant, Endoclinic, Pune.

How does vitamin D affect diabetes?

Dr Kagne adds that researchers have also found an indirect effect of vitamin D on insulin secretion, potentially by a calcium effect on the secretion. “Vitamin D ensures normal calcium flux through cell membranes,” she says. “Therefore, low vitamin D may diminish calcium’s ability to affect insulin secretion, which may contribute to high blood sugar levels. Studies strongly suggest a role of the vitamin D receptor in regulating the transcription of multiple genes, beyond calcium homeostasis (the body maintaining right calcium levels).”

Vitamin D is a fat-soluble vitamin required for muscle as well as bone strength. Dr Bhatt says when somebody is vitamin D deficient, their bone strength and muscle activity may not be as good as of those with good levels of the vitamin, restricting physical endurance. It can, therefore, make management of diabetes difficult too.

Can vitamin D supplements reverse diabetes?

Dr Kagne says many studies have sought to find how many and what kind of vitamin D supplements can help reduce the risk of type 2 diabetes. “But these have been largely inconclusive and have shown the reduction in risk that could be provided by daily vitamin D supplements is minimal,” she says.

Dr Bhatt adds that the medications are different for vitamin D deficiency and diabetes, but measures like healthy lifestyle and proper diet can help manage both together.  

Normal vitamin D levels

Experts say the minimum level of vitamin D a person should maintain for overall health is 20 nanograms per millilitre (ng/mL) or 50 nanomoles per litre (nmol/L). Since that is hard to achieve through diet or sunlight exposure, vitamin D supplements are usually recommended once a week for a couple of months.

“You may opt for foods rich in vitamin D (like fatty fishes, salmon, trout, tuna and halibut) or fortified foods (such as milk and yogurt),” says Dr Kagne.

Dr Bhatt adds that ideally vitamin D has to be produced by the body under the exposure of ultraviolet rays. “Many people think that they are exposed to a lot of sunlight for vitamin D, but ultraviolet rays are not equal to sunrays,” she says. “There is a particular angle of sunlight that maximum part of your body should be exposed to for 20 minutes.”

But the right sun exposure depends on the geography, time zone and the clothing that one wears. Many people also use wear sunscreen lotion, which blocks all the ultraviolet exposure to the skin. “But the fear of skin cancer is also not unreal,” says Dr Bhatt.


  • Studies show that vitamin D deficiency can lead to diabetes.
  • Vitamin D deficiency can cause inflammation — and hence insulin resistance.
  • Vitamin D is required for bone and muscle strength. So, its deficiency can reduce physical endurance and affect diabetes management.
  • Certain food and good exposure to UV rays can help body produce optimum levels of vitamin D.
  • Proper exercises and good lifestyle can help one manage both diabetes and vitamin D deficiency.

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