Illustration depicting foods rich in vitamin d including eggs, mushrooms and salmon.
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Despite being known for sunny weather and outdoor lifestyle, vitamin D deficiency is a common condition in Australia. According to a study published in the Medical Journal of Australia, an estimated 31% of adults in Australia have inadequate vitamin D status, increasing to more than 50% in women during winter–spring and in people residing in southern states.


Vitamin D, sometimes called the “sunshine vitamin,” is both a nutrient we eat and a hormone our bodies make. It is a fat-soluble vitamin that has been shown to help the body absorb and retain calcium and phosphorus – both of which are essential for building strong bones. Additionally, studies have found that vitamin D can reduce cancer cell growth, help control infections, and reduce inflammation.


Unlike other vitamins we absorb through the food we eat, vitamin D is uncommon in most natural food sources; one main exception being the liver of fatty fish, such as salmon. Instead, the body can produce vitamin D from sun exposure. The process starts by taking a modified molecule of cholesterol and exposing it to sunlight in the skin. The ultraviolet (UV) rays in the sunlight provide energy to change the molecule into cholecalciferol, or vitamin D3.


As people spend more time indoors and reduce sun exposure due to the risk of skin cancer it is becoming increasingly difficult to meet required vitamin D levels to keep our bodies working optimally, resulting in a vitamin D deficiency. Some studies have found that almost half of adults have a level below the normal range, meaning that they may benefit from supplementation. In addition, some groups are at greater risk, including infants and the elderly, especially during winter.


Suspected vitamin D deficiency can be confirmed by a simple blood test and there are two factors to consider if supplementation is deemed necessary, says Dr Susan Williams, a physician at Cleveland Clinic’s Endocrinology and Metabolism Institute in the United States. “First, there are two types of vitamin D supplements, namely vitamin D2 and vitamin D3. While both types have been found to increase vitamin D levels, recent studies have indicated that vitamin D3 has a more potent effect over time. Second, we need to consider how the supplement is taken. Recent studies in this regard have indicated that supplements are more effective at raising vitamin D levels when taken with a meal that includes at least 15g of fat. More simply stated, taking the supplement with one’s largest meal appears to promote improved absorption,” she says.

Some people may have problems absorbing vitamin D supplements, says Dr Williams. This includes people with irritable bowel disease (IBD) and coeliac disease. If you suspect you are low in vitamin D, speak with your GP about how to proceed. Problems with absorption can be confirmed through blood tests by comparing the levels of vitamin D in blood taken immediately before an oral dose of vitamin D is given and 12 to 24 hours afterwards. If malabsorption is confirmed, phototherapy may be used, which involves careful skin-typing and carefully metered exposure to UV-B light to increase D levels.

Dr. Williams warns patients against trying to increase their vitamin D by using tanning beds or spending hours sunbathing as this can be ineffective and carries the risks of skin damage and skin cancer.

“Sunshine is composed of approximately 95% UV-A and 5% UV-B, but only UV-B is required for vitamin D synthesis. UV-A is the predominant or sole light source used in tanning beds, and the dose of UV-A in tanning beds can be up to 12 times that provided by the sun,” she says. “UV-A and UV-B are both implicated in skin cancers. UV-A is thought to damage skin and increase the risk of melanoma by causing oxidative stress-induced DNA damage. UV-B damage is more direct, with photoproducts that are implicated in skin carcinogenesis.”

Dr. Williams adds that skin type and age are factors in the response to UV exposure, but in general, exposing 5% of the body surface twice weekly for 20 minutes in warm months may be equivalent to 430 international units (IU) of vitamin D per day, but a plateau is reached after 20 minutes, so time in the sun should be limited given the associated risks.