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Vitamin D

Vitamin D is a ‘sunshine’ vitamin that you get it for free under sunlight. But what is vitamin D for? Apart from sunlight, how can I get it? 

Vitamin D is a fat-soluble vitamin that promotes the absorption of calcium, regulates bone growth and plays an important role in immune function.

Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) are the two forms that most seen. 

vitamin d function - enhance efficiency of innate immunity

When facing harmful bacteria, fungi and viruses that enters us, our body has natural killer cells and macrophages, along with other immune cells, recognize, engulf and destroy pathogens. They are like soldiers that fight to destroy the enemy’s camp.

When the innate immune system is activated, Vitamin D binds to certain cells to enhance the expression, transformation and promote the efficiency in killing pathogens, thus helping the innate immune system to kill viruses. 

vitamin d function - anti-inflammatory and calms adaptive immune system

Cells of the adaptive immune system produce cytokines – small proteins that attract more immune cells and trigger inflammation. But sometimes, cytokines may become too abundant and create a cytokine storm – when immune cells spread beyond infected body parts and attack healthy tissue.

Vitamin D provides anti-inflammatory effect by binding to the cells of the adaptive immune system and turns some genes on while switching others off. Vitamin D calms the adaptive immune system, causing cells to produce fewer cytokines, reducing inflammation and the possibility of cytokine storm. 

COVID-19 & Vitamin D

COVID-19 (SARS-CoV-2) viruses induces cytokine production and pro-inflammatory responses. High levels of cytokine storm syndrome may be one of the critical hallmarks of COVID-19 disease severity. As mentioned above, vitamin D can reduce the possibility of cytokine storm. Vitamin D, with ample evidence, is essential for normal immune and lung functions to fight pathogens and prevent autoimmune diseases.

An inverse correlation was demonstrated between the level of vitamin D and the risks of COVID-19 infection and of severe disease in those infected. This means the lower level of vitamin D will have higher risk of COVID-19 infection and severe disease.

Studies found that people with vitamin D deficiency were 14 times more likely to have a severe or critical case of COVID-19. The mortality rate for those with insufficient vitamin D levels was 25.6%, compared with 2.3% among those with adequate levels. 

The latest research suggested the potential of vitamin D supplementation to prevent acute respiratory infection by keeping the immune system balanced, just like a gymnast walking on a balance beam.

How to get vitamin D

When our body is under the sun, ultraviolet B (UVB) radiation from sunlight triggers the formation of vitamin D3 in skin, and our body knows how to balance itself so that it doesn't accumulate excess vitamin D from prolonged exposure.

But note that UVB cannot penetrate glasses and enter indoor, so we have to get out and enjoy the sunlight! Applying sunscreen will also block UVB from entering the skin, so it is recommended that you only apply it to your face, leaving some space on your hands and feet to allow your skin to make some vitamin D for you!

Apart from exposing to sunlight, we can obtain vitamin D through our diet. Vitamin D3 is only found in animal-sourced foods, whereas D2 mainly comes from plant sources.

Essential Daily Intake

It is best to get vitamin D from food and exposing to sunlight. 

An Australian study found around 10–15 minutes of sun exposure at around 10:00 or 15:00 three to four times per week should be enough for fair-skinned people to produce recommended vitamin D levels. Longer the exposure time, more the vitamin D produced? Sorry no. If exposed to the sun for more than 15 minutes, the sunlight will convert the vitamin D that has been generated under the skin and metabolize them into other substances. The effective absorption time is found to be 15 minutes.

The recommended daily value is 800 IU (20 mcg) of vitamin D per day from foods. If you don’t get enough sunlight, your intake should likely be closer to 1,000 IU (25 mcg) per day.

Since vitamin D is fat-soluble, it is best absorbed when taken with a meal or snack that includes some fat.

However, for those that look for vitamin D supplementation, you have to be aware of overdosage. It is recommended to test the level of vitamin D in your blood before you take any supplementation.