Importance of Vitamin D for Humans

Introduction
Vitamin D, a fat-soluble vitamin absorbed with dietary fats, gets stored in the fatty tissues, including the liver. One will be surprised to know that Vitamin D is not a vitamin but a prohormone (a hormone precursor). Vitamin D exists in several forms, i.e., Vitamin D1, Vitamin D2, Vitamin D3, Vitamin D4, and Vitamin D5. Vitamin D2 (ergocalciferol) and Vitamin D3 (Cholecalciferol) are the essential compounds of Vitamin D that are useful to humans. When we say Vitamin D, it refers to either D2 or D3, collectively called calciferol. Vitamin D enters our body inactive and activates protein enzymes in the liver and kidneys. Vitamin D receptors modulate the gene expression of transport proteins inside our body, which helps in calcium absorption in the intestine. The Vitamin D receptors are expressed by cells of many organs in the human body like the brain, heart, prostate, skin, breast, and gonads. Vitamin D is essential to the human body for many reasons.
This article describes, in brief, those critical roles of Vitamin D along with the essential sources of Vitamin D.

Role of Vitamin D in humans
The significant role of Vitamin D is that it helps in the absorption of calcium and promotes bone growth. It also maintains the health of our teeth. In addition, an abundant quantity of Vitamin D in the body prevents rickets in children and Osteomalacia in adults.
Vitamin D regulates the immune system, neuromuscular system, maintains phosphorous and calcium levels in the blood, and plays an essential role in the life cycle of human cells. Vitamin D triggers our body’s immune cells to produce antibodies, strengthening the immune system. A randomized controlled trial carried out in school children found that Vitamin D3 supplements during winter reduce the incidence of Influenza A. Similarly, in another article published in the Journal of American Medical Association (JAMA), 2006, the researchers experimented if levels of 25-hydroxyvitamin D are associated with risk of multiple sclerosis. The study found evidence that Vitamin D reduces the risk of multiple sclerosis.
Vitamin D helps in diabetes management by regulating insulin levels. However, few published articles also suggest that Vitamin D in the human body in a sufficient amount decreases the risk of individuals developing high blood pressure, osteoporosis (weakening of the bones), cancer, and many other autoimmune diseases.
Scientists from the Medical Department of University Hospital of North Norway have carried out a study on the effect of Vitamin D in improving the health of people suffering from depression. The study results were published in the Journal of Internal Medicine in 2008. The scientists found that the persons suffering from depression saw a progressive improvement in their health after taking Vitamin D supplements. In addition, some studies also reported that Vitamin D assists in maintaining joint and muscle comfort and maintaining a healthy mood and supports breast, colon, and prostate health.

Significant sources of Vitamin D
The human body produces Vitamin D naturally upon exposure to sunlight. Therefore, people should take morning walks and get exposed to the rising sun’s rays. Exposure of the hands, legs, face, and back to the sun during the early hours of the day helps synthesize plenty of Vitamin D naturally.
However, if you want to take a sunbathe or have jobs in the field that exposes you to sunlight for a longer time, make sure to apply the right sunscreen on your body before moving out.
Vitamin D is present naturally in very few food items like fortified milk products (milk, cereal, and yogurt), shrimp, fortified orange juice, fortified cereals & oatmeal, wild-mushrooms, cod-liver oils, fatty fish ( rohu, trout, tuna, salmon, and herring), egg yolks, and liver. Unadulterated Cow’s milk is rich in riboflavin, calcium, phosphorous, and many other nutrients. If you are lactose intolerant or you do not like cow milk, you can also include Fortified Soy Milk in your diet.
Cod-liver oil is also high in omega-3 fatty acids, which is lacking in many people across the globe. In addition, wild mushrooms have a high content of Vitamin D2 and are the only good non-animal source of Vitamin D.
Cultivated mushrooms contain a tiny amount of Vitamin D. Still, when exposed to UV rays, they become a good source of Vitamin D.
Vitamin D supplemental products are also available in the market in a variety of formulations like capsules, tablets, sublingual tablets, and liquids.

REFERENCES

1. The Truth About Vitamin D: Why You Need Vitamin D? Accessed at
   https://www.webmd.com/osteoporosis/features/the-truth-about-vitamin-d-why-you-need-vitamin-d
2. The Benefits of Vitamin D. Accessed at
   https://www.healthline.com/health/food-nutrition/benefits-vitamin-d#boosts-weight-loss
3. Munger KL, Levin LI, Hollis BW, Howard NS, Ascherio A. Serum 25-Hydroxyvitamin D Levels and Risk of Multiple Sclerosis. JAMA. 2006;296(23):2832–2838. doi:10.1001/jama.296.23.2832
4. Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60. doi: 10.3945/ajcn.2009.29094. Epub 2010 Mar 10. PMID: 20219962.
5. Jorde, R., Sneve, M., Figenschau, Y., Svartberg, J., & Waterloo, K. (2008). Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial. Journal of internal medicine, 264(6), 599-609.
6. Vitamin D. Accessed at https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
7. The Important Role of Vitamin D. Accessed at
   https://www.pharmacytimes.com/view/otcfocusvitamind-0210