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Vitamin D: Essential for boosting immunity

Dai Mang Ting, HK BioTek Nutritionist

Vitamin D is one of the micronutrients that play a role in calcium absorption, bone and dental health, eczema management, reducing of respiratory and intestinal tract infections, etc. These functions are associated with maintaining a normal immune system and autoimmunity, especially during a pandemic. However, the public awareness of this aspect is still insufficient.

The main functions of vitamin D include:

  • Assists in the absorption of calcium and magnesium, strengthens the bone and dental health, and prevents osteoporosis.

  • Boosts the immune system, helps with eczema management, reduces respiratory and intestinal tract infections, and inflammation.

  • Regulates cell growth, neuromuscular functions, and prevents muscle twitching.

  • Regulates mood management and reduces the risk of depression and anxiety.

According to a survey conducted by a local university in 2018, about 80% of young adults have low levels of vitamin D. In addition, vitamin D levels in children are also below international standards. Under the pandemic, studies have found that most of the confirmed patients have insufficient vitamin D levels or even suffer from vitamin D deficiency. Compared with the normal individuals who have adequate vitamin D status, low levels of vitamin D tend to lead to a higher risk of severe illness. Moreover, insufficient vitamin D is more likely to cause inflammation including chronic inflammation, intestinal inflammation, rheumatoid arthritis, respiratory diseases, in the body.

Indeed, vitamin D is mainly made from sunlight exposure. Our body can stimulate the vitamin D synthesize through UV light. Despite it is widely believed that vitamin D can be adequately absorbed with daily exposure to sunlight, the levels of vitamin D is still generally deficient.

Although the pandemic control measures have been relaxed recently, most citizens are preferring to stay indoors or shady places. Some people will apply sunscreen products, hide in indoor or shady places, avoiding being exposed to the sun in hot weather. Besides, children are busy with classroom work and various interest classes, and they prefer indoor sports. All the factors above may reduce the chance of exposure to sunlight, making it impossible for the body to synthesize enough vitamin D through sun exposure.

Recently, people are not going out frequently under an extraordinary period. Apart from the sunlight exposure, how can we get enough vitamin D? In fact, we can get adequate vitamin D by following ways:

  • Sunlight Exposure

Vitamin D is mainly synthesized by human body under proper sunlight exposure. It is recommended to do more outdoor activities or bask to the sunlight for 10 – 15 minutes a day. The best time is between 11:00 to 13:00. Bear in mind please do not apply sunscreen products because it might affect the vitamin D synthesis.

  • Diet

Vitamin D is a fat-soluble vitamin. Consider frying or adding healthier oils such as olive oil and canola oil when cooking to help the fat absorption in body.

Foods rich in vitamin D including fungi (mushroom), oily fish (salmon and mackerel), dairy products (milk or cheese), and soy products (tofu or soy milk), and fortified foods that fortification with vitamin D (breakfast cereals).

  • Vitamin D supplements

If vitamin D cannot be supplemented by the two methods above, vitamin D supplement is recommended. But bear in mind, you should seek professional advice and assistance if you have any questions.

  • Vitamin D test

Vitamin D test can be considered to understand your own levels of vitamin D if you have doubts about your own vitamin D status. It could be helpful for prevention in advance.


  1. Martens, P. J., Gysemans, C., Verstuyf, A., & Mathieu, C. (2020). Vitamin D’s effect on immune function. Nutrients, 12(5), 1248.

  2. Martineau, A. R., Jolliffe, D. A., Hooper, R. L., Greenberg, L., Aloia, J. F., Bergman, P., ... & Camargo, C. A. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. bmj, 356.

  3. Meltzer, D. O., Best, T. J., Zhang, H., Vokes, T., Arora, V., & Solway, J. (2020). Association of vitamin D status and other clinical characteristics with COVID-19 test results. JAMA network open, 3(9), e2019722-e2019722.

  4. Wang, E. W. L., Pang, M. Y. C., Siu, P. M. F., Lai, C. K. Y., Woo, J., Collins, A. R., & Benzie, I. F. (2018). Vitamin D status and cardiometabolic risk factors in young adults in Hong Kong: associations and implications. Asia Pacific journal of clinical nutrition, 27(1), 231-237.

  5. 26 Side Effects of Low Vitamin D You Need to Know About. Available from:

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