Getting enough vitamin D has become a public health issue. Vitamin D, a fat-soluble vitamin, promotes the absorption of calcium and phosphorus from the gastrointestinal tract to maintain strong bones. Besides weak bones, low blood levels of vitamin D are associated with depression, cancer, heart disease, diabetes, poor immune function, asthma in children, and cognitive impairment in the elderly. Rickets is the softening and weakening of bones in children, usually because of an extreme and prolonged vitamin D deficiency.

Those with digestive diseases such as Crohn’s and celiac disease may not absorb adequate amounts of vitamin D from the intestine. People with dark skin produce less vitamin D from sunlight. Obese people require more vitamin D compared to those of normal weight. Vegans are at high risk of vitamin D deficiency because they don’t eat fish or drink vitamin D fortified milk.

The problem is that vitamin D is not naturally present in many foods. It is sometimes added to foods or it’s available as a supplement. The body naturally produces vitamin D when ultraviolet rays from sunlight strike the skin and trigger synthesis. Researchers suggest approximately 5 to 30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen. Individuals with limited sun exposure need to include good sources of vitamin D in their diet. Under the guidance of a physician, those with low blood levels may need to take a supplement to achieve recommended levels of intake.

The table below lists the most recent RDAs (Recommended Dietary Allowances) for vitamin D, which is the average daily level of intake sufficient to meet the nutrient requirements of nearly all (97 percent to 98 percent) healthy people. AI (Adequate Intake) is established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy. These values are based on minimal sun exposure.

Recommended Dietary Allowances (RDAs) for Vitamin D, published in 2010 by US Institute of Medicine

Age Male Female Pregnancy Lactation
0–12 months* 400 IU(10 mcg) 400 IU(10 mcg)
1–13 years 600 IU(15 mcg) 600 IU(15 mcg)
14–18 years 600 IU(15 mcg) 600 IU(15 mcg) 600 IU(15 mcg) 600 IU(15 mcg)
19–50 years 600 IU(15 mcg) 600 IU(15 mcg) 600 IU(15 mcg) 600 IU(15 mcg)
51–70 years 600 IU(15 mcg) 600 IU(15 mcg)
>70 years 800 IU(20 mcg) 800 IU(20 mcg)

* Adequate Intake (AI)

The best dietary sources of vitamin D are fish liver oils and the flesh of certain fish like salmon and swordfish. Egg yolks, and cheese provide some vitamin D.

Mushrooms exposed to ultraviolet light under controlled conditions produce vitamin D2. Recent research supports that eating these types of mushrooms can be as effective as taking a vitamin D3 supplement. These types of mushrooms may in fact become the next superfood trend, especially for vegans since this is one of the only vegan dietary sources of vitamin D. Typically supplements contain Vitamin D3, an animal-derived product, which is unacceptable for vegans. (See chart above for vitamin D content of mushrooms.)

Almost all of the milk supply in the US is voluntarily fortified with vitamin D. Canadian law mandates that milk be fortified. Dairy products made from milk like yogurt and ice cream may not be fortified. Infant formulas are required to be fortified both in the US and Canada. In the 1950s, in Europe, many countries forbid fortification of dairy and food products except breakfast cereals and margarine because of an outbreak of vitamin D intoxication in infants. In the UK milk is not fortified with vitamin D.

In supplements and fortified foods, vitamin D is available in two forms, D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D2 is a fungus/yeast-derived product, manufactured by exposing foods to ultraviolet light. Vitamin D3 is an animal-derived product, manufactured from lanolin, which is the fat of lamb’s wool.

Vitamin D supplements have the potential to interact with several types of medications. Examples include steroids such as prednisone, weight-loss medications such as orlistat, cholesterol-lowering drugs such as cholestyramine (brand names Questran®, LoCholest®, and Prevalite®) and other drugs used to control epileptic seizures. Therefore, it is important to review your medications and supplements with a pharmacist.

According to my book Beyond The Mediterranean Diet, the Swiss have the 2nd longest lifespans in the world, which may be linked to an active outdoor lifestyle and a high vitamin D diet. To learn more about Beyond The Mediterranean Diet: European Secrets of the Super-Healthy, pick up a copy of the book on Amazon.com, BarnesandNoble.com or on my website WorldRD.com.

Bon Appétit!