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On Call: Health Advice from UC San Diego Health Experts

By Lawrence Friedman

When is it Appropriate to Take a Vitamin D Supplement?

Vitamin D is an essential micronutrient that plays a vital role in our body. The classical function of this vitamin is to support a healthy bone mass. In addition, substantial scientific evidence has linked low levels of vitamin D to an increased risk of cardiovascular diseases, cancer, diabetes, metabolic syndrome, depression and compromised immune function.

Vitamin D blood levels are affected by several intertwining factors including age, race, skin type, food intake, sunlight exposure, parathyroid hormone levels and obesity. It is affected by the presence of pre-existing health conditions that compromise vitamin D absorption and metabolism, such as pancreatic, liver, kidney and bowel diseases. Higher vitamin D has been seen in individuals who exercise more frequently.

It is estimated that 70 percent of Americans are vitamin D insufficient. People with a low vitamin D level need to be on a vitamin D supplement. The recommended intake of vitamin D is 600 International Units (IU) per day for ages 1 to 70. People age 70 and older need 800 IU/day while newborns and children up to 12 months need 400 IU/day.

The best way to know if you need to be on a supplementation regimen is by checking your levels during your annual lab exams. The supplementation dose is based on the level of deficiency and the presence of pre-existing medical conditions. Once supplementation is started, the levels can be rechecked in six to eight weeks or per your doctor’s recommendation.

When vitamin D levels are normal—with the absence of chronic diseases—intake of high vitamin D foods can be sufficient. If you need to take calcium supplements, consider combined calcium-vitamin D brands. Natural vitamin D is found in very few foods and in limited amounts. However, fatty fish is considered a good source of natural vitamin D. Per 3.5 oz serving: herring contains 680 IU, salmon 360 IU, mackerel 234 IU, sardines 250 IU and tuna 200 IU. Trace amounts are present in cheese, egg yolks and beef liver. Fortified foods, such as juices, milk, yogurt, margarine and breakfast cereals are good sources of vitamin D.

Levels below normal require the intake of extra vitamin D supplements. Vitamin D supplements are found in the two different forms: D2 (ergocalciferol) and D3 (cholecalciferol). Both forms share almost the same metabolic pathways and both increase vitamin D in the blood. However, vitamin D3 is preferred because it is more efficient in raising and maintaining vitamin D levels.

Sunlight exposure is an excellent source of vitamin D, however, exposure should be controlled and in moderation. The efficacy of adequate vitamin D production upon sunlight exposure could be limited by many factors, such as age, skin color, exposed body area, outdoor exposure time and the use of sunscreen. In optimal conditions, outdoor exposure for 10 to 15 minutes twice a week between 10am to 4pm from mid-April to mid-October can form enough amounts of vitamin D to maintain normal levels.

Lawrence Friedman, M.D. Associate Dean for Clinical Affairs, UC San Diego Health. For questions, comments or topic suggestions please contact: +1 619 471 0234 or


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