Vitamin D: 7 Things to Know

Published November 2, 2016

Involved in bone mineralization, vitamin D also plays a role in immune function. How can you meet your needs, where can you find it, and what are its roles? Here is everything you need to know.

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There Are Several Types of Vitamin D

Vitamin D actually includes several types, but the two main (and most active) forms are vitamin D2 and vitamin D3 (cholecalciferol).

Sources of vitamin D are twofold for vitamin D3: diet on one hand, and sun exposure on the other; vitamin D2 comes exclusively from dietary sources (plants).

Vitamin D3 May Help Increase Vitamin D Levels in the Body

Numerous global studies have been conducted on vitamin D, but it is only relatively recently that researchers have compared vitamin D2 and vitamin D3.

Recent studies suggest that vitamin D3 may be more effective than D2, as it may require 2 to 3 times more vitamin D2 than D3 to reach similar vitamin D levels in the body. In addition, vitamin D3 may decline more slowly in the body.

Vitamin D Needs Vary Depending on the Individual

The French Agency for Food, Environmental and Occupational Health & Safety (ANSES) recommends daily intakes (RDI) of around 200 IU for adults and 400 IU for pregnant women, children under 3 years old, and older adults.

However, some experts within the scientific community are now suggesting that RDIs could be increased to 1,000–2,000 IU per day.

Diet and Sun Exposure May Help Meet Vitamin D Needs

Diet and sun exposure are complementary sources of vitamin D. Sun exposure may cover nearly two-thirds of daily needs. However, for the body to synthesize vitamin D from ultraviolet rays, it is generally recommended to expose for 15 to 20 minutes per day (at least arms, hands, and face) between April and October, preferably between 11 a.m. and 3 p.m. Exposure time may vary depending on location and skin type (the further north you live or the darker your skin, the longer exposure may be needed).

Diet provides the remaining intake. Vitamin D3, considered the most effective form, is found in meaningful amounts in cod liver oil, fatty fish, calf liver, eggs, butter, and milk (fortified with vitamin D).

Low Vitamin D Levels Seem Common

Following a multi-year survey, the French Institute for Public Health Surveillance (InVS) estimated in 2012 that nearly 80% of the French population may not meet their vitamin D needs. Among them, more than 40% were reported to have moderate to severe deficiency.

Another study published in the American Journal of Clinical Nutrition found that most Europeans may have low vitamin D levels, both in winter and in summer.

Vitamin D Supplementation May Help Maintain Healthy Bones

Vitamin D is involved in bone mineralization as it may help retain calcium in bone tissues (skeleton, teeth, cartilage).

Vegetarian/Vegan Diets and Vitamin D3 Intake

Since vitamin D3 (of animal origin) is generally considered more effective than vitamin D2 (of plant origin), a diet excluding animal products combined with limited sun exposure (for example in winter) may lead to lower intake.

Vegetarians may obtain vitamin D from fortified milk, butter, or cheese instead of fish, while vegans (who do not consume any animal products) may benefit from considering supplementation.

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