How much Vitamin D do I need?

It may seem that in recent years, everyone is being told they have a vitamin D deficiency. Although it may seem quite unusual for people living in “a sunburnt country” to be lacking a vitamin sourced from sunshine, the evidence is suggesting Australians need more.

So, what exactly is vitamin D?

Vitamin D is a group of fat-soluble compounds that facilitate various physiological functions in our body, from assisting with calcium absorption for strong bones and teeth, to improving immune function against invading viruses and bacteria.

There are 5 different forms of vitamin D. The 2 forms that we’re most interested in are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). Sun exposure will provide us with greater levels of vitamin D3, as ultraviolet light (specifically, ultraviolet B radiation) activates a form of cholesterol in our skin – producing an active form of vitamin D3 for our body to use.

What should I be doing about my vitamin D levels?

For most people, deficiency can be prevented by 5–15 minutes exposure of face and upper limbs to sunlight 4–6 times per week. If this is not possible then a vitamin D supplement is recommended (see below).

In Australia, the prevalence of vitamin D deficiency varies, but is considered to be higher than previously thought. One study found marginal deficiency in 23% of women, and another frank deficiency in 80% of dark skinned and veiled women. The groups at greatest risk of vitamin D deficiency in Australia are dark skinned and veiled women (particularly during pregnancy), their infants, and older persons living in residential care (posing problems for bone density).

Adequate intake of vitamin D is unlikely to be achieved through dietary means, particularly in the groups at greatest risk, although vitamin D-fortified foods may assist in maintaining vitamin D levels in the general population.

How much vitamin D do I need?

The recommendations for vitamin D intake (based on an assumption of little or no sun exposure) are intended to serve as a guide for good nutrition.

Vitamin D is expressed as international units (IU) or micrograms (µg). The Recommended Daily Allowance (RDA) refers to the intake that covers the needs of >97.5% of the population.

Babies 0-12 months           (400 IU/day or 10 µg/day)

Children and adults            (600 IU/day or 15 µg/day)

Elderly 71 years +               (800 IU/day or 20 µg/day)

Pregnant women                 (600 IU/day or 15 µg/day)

Lactating women                 (600 IU/day or 15 µg/day)

Only a few foods in nature contain vitamin D, generally in the form of vitamin D2. The flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources. Small amounts of vitamin D are also found in cheese and egg yolks. In Australia, margarine, milk and some milk products are now fortified with vitamin D.

The main source of vitamin D for Australians is exposure to sunlight, and therefore, vitamin D levels will vary according to the season and are lower at the end of winter. There is also a need to consider the balance of sun exposure for vitamin D production against the risk of skin cancer.

Interesting Vitamin D Facts:

• The wavelength of sunlight that activates vitamin D (known as ultraviolet radiation B or UVB) does not penetrate glass, so although exposure to the sun through a window can cause sunburn, it will not produce vitamin D.

• People with dark skin require longer periods of sun exposure for vitamin D production than people with lighter skin. This is because the skin’s pigment, melanin, prevents UV radiation from penetrating the skin and producing vitamin D.

• Breast milk contains anywhere from <25 IU/L to 78 IU/L of vitamin D, which is well short of the recommended 400 IU/day. We can see that newborns and infants require some sunshine to maintain recommended levels for optimal health and wellbeing.

• Together with calcium, vitamin D helps protect older adults from osteoporosis. Vitamin D allows calcium to pass through our intestinal wall and into our bloodstream. This in turn will maintain adequate calcium concentrations for bone strength.

• Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation.

• The vitamin D3 that is activated by the sun’s rays is a weak form of vitamin D. This weakened form, known as 7-dehydrocholesterol, is transported to the liver and kidneys and converted to a potent form of vitamin D3 by liver and kidney enzymes.