The Health Impact of Vitamin D

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Vitamin D is often known as the sunshine vitamin because ultraviolet rays from the sun cause our skin to produce it. Vitamin D is a fat-soluble vitamin that plays many important roles in our body, including in our immune system.

Vitamin D and the Immune System

Before effective antibiotics were discovered and routinely used to treat infections, people with tuberculosis were sent to sanatoriums where treatment included exposure to sunlight that was thought to kill tuberculosis. It’s now believed that Vitamin D produced from UV sunlight on the skin played an important role in curing tuberculosis. Cod liver oil is also naturally high in vitamin D and was for many years used as a treatment for tuberculosis and other illnesses.

The innate immune system is our body’s first defense against infection and includes physical barriers (skin, mucus membranes), enzymes, antimicrobial proteins, and cell receptors that recognize and destroy pathogens. Vitamin D regulates the various actions within the innate immune system and is a crucial component for a healthy, active immune system.

Researchers believe that there is an association between people with low Vitamin D levels and increased risk of infection. Epidemiological studies show a close association between people with low blood levels of Vitamin D and chronic disease including cardiovascular disease, diabetes and autoimmune diseases. However, raising body Vitamin D levels through food or supplements has shown inconsistent results in improving our immune system response and improving health. 

How Do I Know My Body’s Vitamin D Level?

The best indicator of vitamin D status is measuring serum concentration of the 25(OH)D, which reflects vitamin D produced in our skin as well as vitamin D from foods and supplements.

However, there is considerable discussion about the optimum amount of 25(OH)D for overall health. Based on its review of data of vitamin D needs, a committee from the Institute of Medicine concluded that 25(OH)D from 30-50 nmol/L is sufficient for 97.5% of the population. Serum concentrations >125 nmol/L (>50 ng/mL) are associated with potential adverse effects that can include anorexia, weight loss, polyuria, heart arrhythmias, greater risk of cancer at some sites like the pancreas, greater risk of cardiovascular events, and more falls and fractures among the elderly.

It’s nearly impossible to consume too much Vitamin D from food, and our body naturally regulates the amount of Vitamin D produced in the skin by UV light. The primary cause of too high levels of Vitamin D is supplements.

How Much Vitamin D Do I Need?

The Recommended Dietary Allowance (RDA) is the average daily level necessary to meet the requirements of 97-98% of healthy people and is based on age and sex.

Infants up to 12 months age need 400 IU, children and adults up to age 70 need 600 IU, and people over age 70 need 800 IU Vitamin D.

By Lynn Grieger, RDN, CDCES, CHWC, CPT

Learn more about food sources of vitamin D, the full impact of sun exposure, and when and how vitamin D supplementation works in the companion post Which Source of Vitamin D Works for You?


  1. U.S. Department of Health & Human Services. National Institutes of Health. Office of Dietary Supplements. Vitamin D Fact Sheet for Health Professionals.  assessed 6-27-20. Updated 3-24-20
  2. Aranow C. Vitamin D and the immune system. J Investig Med. 2011;59(6):881-886. doi:10.2310/JIM.0b013e31821b8755
  3. Wang H, Chen W, Li D, et al. Vitamin D and Chronic Diseases. Aging Dis. 2017;8(3):346-353. Published 2017 May 2. doi:10.14336/AD.2016.1021
  4. American Academy of Dermatology. Vitamin D.,may%20not%20lower%20cancer%20mortality. Accessed 6-29-20. 
  5. Newberry SJ, Chung M, Shekelle PG, Booth MS, Liu JL, Maher AR, et al. Vitamin D and calcium: a systematic review of health outcomes (update). Evidence report/technology assessment No. 217 prepared by the Southern California Evidence-based Practice Center under contract No. 290- 2012-00006-I. AHRQ Publication No. 14-E004-EF. Rockville, MD: Agency for Healthcare Research and Quality, 2014.
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