Vitamin D is essential for healthy tooth, bone, and muscle growth and maintenance. There is also evidence that by binding with receptors in the hair follicles, vitamin D can help maintain hair growth. 

The sun is the primary, natural source of vitamin D. Our skin absorbs UVB rays, and our liver and kidneys create a usable form of vitamin D. Some foods, including egg yolks and fish (like salmon and tuna) provide vitamin D. Other foods like milk are fortified with vitamin D.  

Doctors, even dermatologists, recommend at least 15 minutes daily of exposure to the sun for adequate vitamin D production. You should still use your sunscreen when exposed to the sun. You will get sufficient UVB exposure even when using sunscreen, especially in the warm weather. In the cold, our excess clothing and lack of exposure to direct sunlight may leave us deficient in this essential vitamin. 

A number of factors can affect your level of vitamin D: 

  • The further you live from the equator, the less sunlight and vitamin D. 
  • Air pollution can interfere with the UVB rays that stimulate vitamin D production 
  • Sunscreen is designed to block the UVB rays, but dermatologists still encourage using it because we don’t use enough of it often enough to block all the sun’s rays. 
  • Melatonin, which gives color to your skin and eyes, protects the skin from burning by absorbing UVB rays. The darker the skin color the more time it takes to absorb the UVB rays needed to produce vitamin D. 
  • Body fat absorbs and binds vitamin D and contrary to what was once thought, it remains locked away even when needed. Longer exposure is needed to absorb sufficient UVB rays. 
  • As we age, our bodies’ ability to process UVB rays into usable vitamin D diminishes. By age 70, our ability to produce vitamin D is about half of what it was at age 20.   

Nearly 1 in 4 people in the U.S. have inadequate levels of vitamin D. The following table provides rough ranges for low, normal, and high vitamin D levels for the average adult in nmol/ml (nanomoles per liter) and ng/ml (nanograms per milliliter). 

The symptoms of vitamin D deficiency may be subtle. They include: 

  • changes in mood, including depression or anxiety 
  • frequent fractures 
  • slow wound-healing 
  • hair loss
  • loss of bone density 
  • muscle weakness 
  • new or worsening high blood pressure 
  • constant fatigue 
  • chronic pain 
  • infertility 
  • decreased endurance 

Vitamin D is an essential nutrient for a variety of reasons, particularly for bone health. A person will often get enough vitamin D from sunlight, but if they are at risk for a deficiency, they may benefit from taking a supplement. Consult with your doctor and request a test of your vitamin D level. If it is low your doctor can recommend the correct form and dose for a vitamin D supplement. 

No content on this site should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.