Why vitamin-D is unique?

It takes a longer duration of exposure to the sun for our skin to synthesise enough vitamin D during the winter months

Vitamin D is a unique vitamin

Like other vitamins it is essential to life, however, it’s the only one that we actually don’t have to get from our food – only about 5 to 10 per cent of our vitamin D requirement comes from food.

While there’s some vitamin D in foods such as oily fish, liver and mushrooms that have been exposed to sunlight, the majority of our vitamin D comes from the sun. Hence it is often called the “sunshine” vitamin.

When the skin is exposed to sunlight, ultraviolet B (UVB) rays penetrate the skin and trigger a biochemical reaction that converts cholesterol in the skin to vitamin D. As your lifestyle, your job, where you live, the weather and/or the season all affect how much sun you’re exposed to, they also affect how much vitamin D you’re getting.

During winter, it takes a longer duration of exposure to the sun for our skin to synthesise enough vitamin D. However, many people now work indoors all day, and when they are outside during winter they tend to be covered up to keep warm so hardly any skin is exposed to the UVB rays.

So if you don’t spend much time outdoors in the middle of the day during the winter months, and particularly if you live in the South Island, you may be at risk of vitamin D deficiency in spring.

However, the rays that allow us to produce vitamin D can also cause sunburn, which increases the risk of skin cancer, so it is very important to ensure you don’t get burnt.

Outside of winter, it’s best to avoid sun exposure in the middle of the day when the UV index is highest. It’s also essential that you balance the risks associated with sun exposure, with consideration of your personal and family history of skin cancers and other individual circumstances such as whether you take medications that are photosensitizing.

There are a few factors that can increase the risk of vitamin D deficiency. Melanin in the skin absorbs the UV radiation, so not as much vitamin D is produced in the dark skin when it is exposed to sunlight. Older adults are also at increased risk of deficiency as our ability to produce vitamin D in the skin decreases as we age. Vitamin D can also be sequestered in body fat stores, so people with excess body fat can have lower levels of vitamin D available for use in the body.

Another unique property of vitamin D is that it is actually considered a hormone. Many people are aware of vitamin D’s role in bone health – it increases absorption of calcium and phosphorus and deficiency results in impaired bone mineralisation – however, it does so much more than this.

Vitamin D regulates gene expression, is essential for the immune system and is thought to play a role in blood pressure regulation. It’s also important for healthy muscle function and may affect the risk of depression. A deficiency of vitamin D is also associated with an increased risk of some autoimmune diseases.



  • Immunity Badao – Bimari Bhagao