Guest post by Dr Laura Villa

Did you know that vitamin D deficiency is prevalent? It is estimated that about 1 billion people worldwide have low levels.

Vitamin D is a fat-soluble vitamin, meaning it is absorbed along with fats in the diet and stored in the body’s fatty tissue and the liver. It plays a vital role in the balance of calcium and phosphorus and bone metabolism. Vitamin D has other roles in the body, including reducing inflammation, improving immune function, and helping with blood sugar metabolism. Unlike other vitamins, vitamin D functions like a hormone as well, and every single cell in your body has a receptor for it.

The major sources of vitamin D are exposure of the skin to UVB radiation from the sun and dietary intake.

  • Twenty minutes of sunshine daily with other 40% of skin exposed is required to prevent deficiency.
  • The best dietary sources are fatty fish (mackerel, sardines, and salmon) and fortified foods like milk. Because it is fat-soluble, it does not dissolve in water and is best absorbed when paired with high-fat foods — avocados, nuts, seeds, eggs, etc.

Vitamin D deficiency can result from several causes:

  1. Decreased dietary absorption. Vitamin D requires no digestion and is absorbed in the small intestine, so conditions that affect that area, like celiac disease and inflammatory bowel disease, would decrease absorption.
  2. Decreased sun exposure and using sunscreen. About 80% of vitamin D is absorbed through the skin, while the rest comes from diet.
  3. You have dark skin. The pigment melanin reduces the skin’s ability to make vitamin D in response to sunlight exposure.
  4. Your kidneys cannot convert vitamin D to its active form. As people age, their kidneys are less able to convert vitamin D to its active form, thus increasing their deficiency risk.
  5. Age. The skin’s ability to make vitamin D lessens with age.
  6. Medications. Levels can be lowered by certain medications like laxatives, steroids, cholesterol-lowering drugs, etc.

Signs that you might be deficient:

  • Getting sick often
  • Feeling fatigued
  • Bone pain or back pain
  • Depression
  • Hair loss
  • Muscle pain

The dosing of vitamin D depends on the severity of the deficiency. However, a good maintenance dose is between 1000 to 2000 international units. Because vitamin D is fat-soluble, toxicity is possible, although rarely noted. So please consult your doctor before beginning supplementation.

  1. References:
  3. Sizar O, Khare S, Goyal A, et al. Vitamin D Deficiency. [Updated 2020 Jul 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. 
  4. Chen TC, Chimeh F, Lu Z, et al. Factors that influence the cutaneous synthesis and dietary sources of vitamin D. Arch Biochem Biophys. 2007;460(2):213-217. doi:10.1016/
  5. Maurya VK, Aggarwal M. Factors influencing the absorption of vitamin D in GIT: an overview. J Food Sci Technol. 2017;54(12):3753-3765. doi:10.1007/s13197-017-2840-0
  6. García JD PhD. Vitamin D. Salem Press Encyclopedia of Health. 2019. Accessed February 9, 2021.