Vitamin D

Vitamin D
Vitamin D is a fat-soluble vitamin that can be found in food such as fatty fish (mackerel, tuna and salmon) and dairy products. Vitamin D is unique from the other vitamins, since it’s the only vitamin besides B3 that humans can synthesize. the others have to come from our diets or injections. Vitamin D is produced in our skin when exposed to sunlight. Our skin produces the amount of vitamins needed, but in darker seasons in certain areas (like winter in the northern-hemisphere) when there is a lack of sunlight, larger amounts should be implemented in our diets.

Vitamin D is needed for the absorption of calcium and strengthening of bones.

Vitamin D deficiency is a common problem in places where sunlight is limited, such as northern parts of the world. Symptoms may include bone pain and muscle weakness. In more severe cases, there can be a loss in  bone density, and can lead to fractures and osteoporosis.

Sources:

https://www.quora.com/Which-vitamin-can-be-synthesized-by-the-human-body

https://www.webmd.com/food-recipes/guide/calcium-vitamin-d-foods

https://www.vitamindcouncil.org/about-vitamin-d/how-do-i-get-the-vitamin-d-my-body-needs/