The post The Health Impact of Vitamin D covered the key role that vitamin D plays in the immune system, along with research about its health impacts. But how exactly can you get enough vitamin D, and which sources will be best for you? Well, that's what this post is all about!Remember, the RDA for most children and adults is 600 IU of vitamin D daily. Infants under age 1 need only 400 IU, while seniors over age 70 need 800 IU each day.What Foods Contain Vitamin D?Very few foods naturally contain Vitamin D. The best sources are rainbow trout, salmon, sardines and tuna. Beef liver, cheese, and egg yolks contain smaller amounts of Vitamin D.Fortified foods with added Vitamin D provide most of the Vitamin D we consume. Almost all of the U.S. milk supply, including dairy milk as well as plant milks such as soy, almond, and rice milks, is voluntarily fortified with 100 IU per cup. Mushrooms exposed to ultraviolet light under controlled growing conditions also contain higher levels of Vitamin D.Exactly How Much Vitamin D is in a Serving?

• Rainbow trout, 3 oz cooked: 645 IU
• Sockeye salmon, 3 oz cooked: 570 IU
• White mushrooms exposed to UV light, ½ cup: 366 IU
• Milk, dairy and plant-based, fortified, 1 cup: 100-144 IU
• 1 egg yolk: 44 IU

How Much Vitamin D Do I Get From Sunlight?There are several factors that affect UV sunlight exposure and vitamin D synthesis in our skin: season of the year, time of day, cloud cover (complete cloud cover reduces UV by 50%), smog (severe smog can reduce UV by 60%), and skin melanin content.UV light does not go through glass windows, and shade also blocks UV light. Sunscreen with a sun protection factor (SPF) of 8 or more blocks vitamin D-producing UV rays when applied correctly.Vitamin D produced in the skin from UV light is stored in the liver and body fat, and 5-30 minutes of sun exposure between 10am and 3pm twice each week to the face, arms, legs or back without sunscreen usually leads to sufficient Vitamin D production.Caution: The same UV light that synthesizes Vitamin D in our skin is also a carcinogen responsible for most of the estimated 1.5 million skin cancers and the 8,000 deaths due to metastatic melanoma that occur annually in the United States. Lifetime cumulative UV damage to skin is also largely responsible for some age-associated dryness. There are no studies to determine whether UV-induced synthesis of vitamin D can occur without increased risk of skin cancer. The American Academy of Dermatology (AAD) recommends getting vitamin D from a healthy diet that includes foods naturally rich in vitamin D, foods and beverages fortified with vitamin D, and/or vitamin D supplements and not from sunlight due to the potential increased risk of skin cancer.Should I Take Vitamin D Supplements?Before taking Vitamin D supplements, be sure to talk with your physician. Vitamin D is available in two forms in both supplements and fortified foods. D2 (ergocalciferol) is made by UV irradiation on yeast, and D3 is made by UV irradiation on lanolin found in sheep’s wool. There is no firm research that shows benefits of one form over the other, but at higher doses, D2 is less effective.Some groups of people are known to have higher risk of low levels of Vitamin D. They include...

• Breastfed infants because human milk is typically low in Vitamin D. The American Academy of Pediatrics recommends that exclusively and partially breastfed infants be supplemented with 400 IU of vitamin D per day. Note: The Vitamin D content of breastmilk can be higher in women who use Vitamin D supplements; be sure to follow your pediatrician’s recommendations.
• Older adults because as we age, our skin is less able to synthesize Vitamin D from sunlight.
• People with limited exposure to sunlight.
• People with darker skin because larger amounts of the pigment melanin in the epidermal skin layer result in darker skin and reduce the skin’s ability to produce vitamin D from sunlight.
• People who are obese because greater amounts of subcutaneous fat alter the release of Vitamin D into circulation.
• People who have had gastric bypass surgery since part of the upper small intestine where vitamin D is absorbed is bypassed in the surgery and vitamin D mobilized into the serum from fat stores may not compensate over time.

Vitamin D Tips:

• Even though research shows an association between low body levels of Vitamin D and decreased immunity, there is no conclusive evidence that raising body Vitamin D levels with food, supplements, or sunlight has a direct benefit on immunity.
• However, adequate amounts of Vitamin D are important for strong bones, cell growth modulation, and neuromuscular functions. Regularly consuming foods that contain Vitamin D, either naturally or through fortification, is part of a comprehensive approach to health.
• It’s best to get Vitamin D from food and only use supplements upon the advice and recommendation of your physician to avoid too high body levels of Vitamin D, which can be dangerous to health.

By Lynn Grieger, RDN, CDCES, CHWC, CPTReferences:

1. U.S. Department of Health & Human Services. National Institutes of Health. Office of Dietary Supplements. Vitamin D Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/  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. https://www.aad.org/media/stats-vitamin-d#:~:text=The%20AAD%20recommends%20getting%20vitamin,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.