The sunshine vitamin paradox!

Vitamin D is known as the ‘sunshine vitamin’ as exposure to sunlight stimulates vitamin D production in the skin. Now, one might assume that vitamin D deficiency would be rare in a country like India that receives adequate sunlight through the year. Unfortunately this is not the case, the prevalence of vitamin D deficiency in India has been reported to be between 80%-90% !

Image from Laura Lockaua & Stephanie A.Atkinson (2018)

Vitamin D is a fat soluble vitamin that functions like a hormone. It is produced in the skin on exposure to sunlight (ultraviolet B rays), where UV radiation causes the conversion of 7-dehydrocholesterol (in skin) to vitamin D3 (the active form). We can also get vitamin D directly from our diet.

Vitamin D3 has a number of important physiological functions, out of which the most vital are regulating the absorption of calcium & phosphorous levels in the body to maintain bone homeostasis. When you have insufficient vitamin D, the amount of dietary calcium that is absorbed is reduced. This is important because calcium is essential for muscle contraction, cell signalling, development of teeth & bones, and regulating heart beat & fluid balance.

The reason vitamin D is in the spotlight is because it plays a vital role in both health and disease. More recent data has shown that there is a connection between sub-optimal vitamin D levels & a number of non-bone related health outcomes such as; cardiovascular disease, elevated blood pressure, low immunity, glucose metabolism disorders, rheumatoid arthritis, certain autoimmune disorders, inflammation, weight gain and even certain mood disorders.

So why is vitamin D deficiency so prevalent in India?

• Reduced exposure to sun: temperatures in India can get pretty high and hence it’s understandable that most people don’t enjoy standing in the sun for too long. This in combination with an aversion to skin darkening results in minimal exposure to the sun. However, it’s not as simple as standing out in the sun whenever you please; the time of sun exposure is very important. A study by Harinarayan et al (2013) found that the synthesis of vitamin D3 is maximum between 11:00am and 2:00pm all year round in India.
• Skin pigmentation: melanin is the pigment that gives colour to our skin, (i.e. the darker your skin the more melanin you have) and it protects the skin from UV radiation. Hence, the amount of melanin in your skin affects how much vitamin D you produce. Which means that if you are darker skinned, less UVB will get through your skin and hence less vitamin D is produced. Essentially a darker skinned individual will require more time in the sun to make the same amount of vitamin D as compared to a fairer skinned individual.
• Dietary factors: a number of Indians are vegetarians and hence their intake of vitamin D from animal sources is low. While fortified milk is a good source of vitamin D for vegetarians, milk in India is rarely fortified with vitamin D.
• Age: as we age, the ability of our body to synthesise vitamin D reduces. This reduction in synthesis begins between 65 to 70 years of age and is associated with the malabsorption of calcium which is also a natural outcome of age-related decline in renal function.
• Body fat: a number of studies have found an association between obesity & low vitamin D levels. A possible mechanism behind this association is that vitamin D gets trapped or hidden within the adipose tissue and hence the amount freely available in the blood is reduced. It’s important to mention that whilst obesity has been identified as a factor in the development of vitamin D deficiency, vitamin D deficiency has not been identified as a factor in the development of obesity.
• Influence of medication: certain drugs (cholesterol-lowering drugs, steroids, anti-epileptic drugs, Clotrimazole, Rifampici, & fat blockers like orlistat) can negatively impact the metabolism and absorption of vitamin D. It is important to always tell your doctor/nutritionist about the medication & supplements (including herbal) you take so that they can look out for contraindications.

Key take aways to optimise Vitamin D levels:

• Check your vitamin D levels regularly: make sure to include vitamin D testing in your routine check up as you may not notice the symptoms of deficiency.
• Supplement if deficient: if your vitamin D levels are very low, then supplement with vitamin D under the guidance of a healthcare professional. Depending on your age it maybe advisable to supplement concurrently with calcium as prolonged vitamin D deficiency can affect bone health.
• Get adequate sun exposure: the recommendation is to expose bare skin to the sun between 11am and 2pm for 30minutes thrice a week. Try to spend more time outdoors, earthing is a good activity to begin with . If sunshine isn’t working in your favour, then include vitamin D rich foods in your meals or supplement with vitamin D.
• Eat Vitamin D rich foods: help your body get more vitamin D by eating generous portions of vitamin D rich foods, such as: oily fish (like Rawas-Indian salmon, Indian carp, mackerel, sardines), cod-liver oil, egg yolk, fortified milk, tofu and meat. Calcium is also important for bone health and hence you must include calcium rich foods such as green leafy vegetables, fish, tofu, almonds, chia seeds, white beans, yogurt, sesame etc regularly.
• Incorporate regular exercise: A number of studies have found that vigorous physical activity is a modifiable contributor to vitamin D status & that regular exercise can assist with the synthesis of vitamin D. Exercising a minimum of 30 minutes 3–4 times a week is a good place to start!