The Importance of Vitamin D and Safe Ways to Get It
Last updated: July 2018
Vitamin D is a fat-soluble vitamin that can be produced in the body when the skin is exposed to sunlight. There are not many foods that contain vitamin D, but it is available as a dietary supplement.
Why we need vitamin D
Vitamin D is important for health and plays many important roles in the body, including:
- Promoting calcium absorption in the gut
- Bone growth and remodeling (the ongoing process of bone regeneration)
- Regulation of cell growth
- Proper immune system functioning
- Reducing inflammation
Vitamin D plays an important role in preventing osteoporosis, a disease that causes brittle, fragile bones and commonly affects older adults. Although osteoporosis is associated with insufficient intakes of calcium, vitamin D is necessary for the body to absorb calcium. In addition, several studies suggest that vitamin D can reduce a person’s risk of developing cancer, including cancers of the breast, colon, and prostate.
Foods containing vitamin D
Vitamin D is present in fatty fish, including salmon, tuna, and mackerel. Small amounts of vitamin D are found in beef liver, cheese, egg yolks, and some mushrooms. The majority of vitamin D that comes from diet is due to fortified foods, including milk, some breakfast cereals, and some brands of orange juice or yogurt.
Vitamin D deficiency
A deficiency in vitamin D may occur if there is inadequate dietary intake over time or exposure to sunlight is limited. A vitamin D deficiency can cause rickets in children, a disease in which the bone tissue doesn’t mineralize properly, creating soft bones and skeletal deformities. In adults, a vitamin D deficiency can lead to weak bones called osteomalacia.
People who are at risk for a vitamin D deficiency include:
- Those who follow a vegan or ovo-vegetarian diet
- People who are lactose intolerant or who have a milk allergy
- Infants that are breastfed
- Older adults, because their skin doesn’t synthesize vitamin D as efficiently
- Those with limited sun exposure, including people who wear long robes and head coverings for religious reasons
- People with dark skin since the pigment melanin reduces the skin’s ability to produce vitamin D
- People with inflammatory bowel disease (including Crohn’s and ulcerative colitis) and other conditions that cause fat malabsorption
- People who are obese or who have had gastric bypass surgery
How much vitamin D do you need?
The Recommended Dietary Allowance (RDA) is an average daily level that is sufficient to meet the nutrient requirements of most healthy people. The RDAs for vitamin D are:
- For children 0-12 months of age: 400 International Units (IU) (10 micrograms (mcg)
- For children 1-18 years: 600 IU (15 mcg)
- For adults 19-70 years: 600 IU (15 mcg)
- For older adults over 70 years: 800 IU (20 mcg)
Sun exposure and vitamin D
Most people get some of their vitamin D needs through exposure to sunlight, although the skin’s ability to produce vitamin D may be impacted by the season, time of day, cloud cover, smog, melanin content in the skin, and sunscreen use. All these factors make it difficult to provide general guidelines on how much sun exposure is needed to maintain adequate vitamin D levels. Some researchers have suggested that approximately 5-30 minutes of exposure of the face, arms, legs, or back to the sun between 10 a.m. and 3 p.m. at least twice a week without sunscreen is sufficient to produce adequate levels of vitamin D. However, despite the benefit of vitamin D production with sunlight exposure, experts agree that sun exposure should be limited because of the damaging effects of UV radiation and the risk of skin cancer.
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