Vitamin D Deficiency is Common
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In Brief
- Vitamin D deficiency is common in Australia
- In many cases Australians do not receive adequate vitamin D from casual sun exposure
- Vitamin D is essential for healthy, strong bones and is protective against cancer
- Postmenopausal are at greatest risk of osteoporosis and vitamin D deficiency significantly increases the risk
- Many women I see in my clinic have low levels of vitamin D
- All adults should be checked routinely for vitamin D deficiency, particularly those in the high risk groups discussed below
- Vitamin D supplementation may be necessary
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What is vitamin D?
Vitamin D is a fat soluble vitamin, also called calciferol and sunlight vitamin. Although small amounts of Vitamin D can be obtained from some foods (see below), the majority of our vitamin D is produced by the body when UV radiation in sunlight hits our skin and reacts with a cholesterol-like substance in the skin. It is the only vitamin that is manufactured in body and is also considered a hormone. After being produced in the skin vitamin D enters the circulation and travels to liver and kidneys where it is synthesised into its active form.
Prevalence of vitamin D deficiency in Australia
The prevalence of vitamin D deficiency in Australia varies, however according to an article in the Medical Journal of Australia it is much higher than previously thought. Studies have shown that vitamin D deficiency is common in the elderly with up to 76% having a marginal deficiency. Other studies have shown that up to 43% of younger adults have inadequate vitamin D levels. The highest rates of severe deficiency occur in dark-skinned, veiled, and pregnant women with a deficiency incidence of up to 80%.
The importance of vitamin D
Adequate levels of vitamin D are essential for healthy, strong bones. Therefore its importance increases in menopausal and postmenopausal women, who are already at risk of developing osteoporosis due to decreased oestrogen levels.
Vitamin D is necessary for calcium absorption and for regulating calcium and phosphate concentrations in the blood, which ensure normal mineralisation of bone. Without sufficient vitamin D bones can become weak and the incidence of fracture may increase.
Ensuring healthy bones is not the only job of vitamin D. It also plays important roles in the health and functioning of the immune system, neuromuscular function and in the reduction of inflammation. In addition, vitamin D plays a role in the prevention and treatment of type 1 and type 2 diabetes, hypertension, glucose intolerance, autoimmune thyroid disease and multiple sclerosis.
Vitamin D deficiency and increased cancer risk
Vitamin D has potent anticancer properties and vitamin D deficiency may be associated with an increased incidence of a number of cancers, particularly those of the gastrointestinal tract. According to a study published in 2008, low vitamin D status may increase breast cancer risk in post-menopausal women. 4 Vitamin D may also play a role in the outcome for cancer patients.
Vitamin D deficiency in children
In recent times vitamin D deficiency has re-emerged as a significant health issue in children. This can result in seizures (due to low calcium), limb pain, fractures and rickets.
Vitamin D deficiency in pregnant women will result in a deficiency in their infants. Therefore all women considering pregnancy should have their vitamin D levels checked before conception and during pregnancy.
What causes vitamin D deficiency?
The major cause of vitamin D deficiency is inadequate exposure to sunlight. This is a difficult issue because we also know that too much sun exposure can lead to skin cancer and malignant melanoma. It is quite ironic that scientists now believe that vitamin D is protective against skin cancer. Therefore we may be putting a little too much effort (and money) into protecting ourselves from the sun.
Although you may often read that most Australians get enough sun exposure to ensure adequate vitamin D levels, especially in the more northern parts of Australia, this is not the reality and certainly is not what I see in my clinical practice. Almost every woman I have seen who has had a blood test for vitamin D levels has either been on the low side of normal or outside the normal range, exhibiting a deficiency.
How much sun is enough (but not too much)?
It is difficult to find a definitive answer about the optimal amount of sun exposure which ensures adequate vitamin D levels without causing a risk of skin cancer etc. In actual fact the answer will be quite different for different regions of Australia and for different individuals.
Sun exposure should be limited to the early morning and late afternoon and the amount of exposure needs to suit the individual skin type. Very fair skinned people can tolerate less sun that those with olive skin or darker skin. Indeed people with fair skin actually need much less sun exposure for the production of vitamin D because the UV rays penetrate the skin much easier.
In 2006 the Medical Journal of Australia published information on recommended sun exposure times (at 10am or 3pm) for fair skinned individuals aged 19-50 years with 15% of their body exposed to the sun eg face, arms and hands. As you would expect exposure time varied greatly depending on locality. For example in Townsville as little as 10 minutes in summer and up to 15 minutes in winter, whilst in Hobart up to 13 minutes in summer and as much as 166 minutes in winter may be needed to ensure sufficient vitamin D levels based on current recommended daily allowances.
These recommended times are only estimations and are subject to many variations including seasonal differences in UVB levels from one year to another, altitude, skin type, level of cloud cover etc. It is also worth noting that many researchers have suggested that optimal vitamin D intake has been underestimated and that official recommendations are too low. If this is the case recommended sun exposure times may be too short, however excessive unprotected sun exposure may increase risk of skin cancer.
The best way to ensure that you have adequate vitamin D is to have yearly or twice yearly blood tests to check your vitamin D status. Try to ensure adequate sun exposure without overdoing it. You need to be careful and take your skin type, your location, time of day and season into account. If the exposed area begins to redden slightly it is time to get out of the sun.
Those at most risk of vitamin D deficiency
Older adults
As we age the skin is less able to produce vitamin D and the kidneys are less efficient at converting it into the active form. The risk of vitamin D deficiency is increased for older people who spend most of their time indoors.
People with limited sun exposure
People who are homebound and women who wear veils and/or long robes are very likely to have vitamin D deficiency. Many people get very little or no sun exposure during winter, particularly on their working days. Vitamin D supplementation may be necessary during the winter months.
People with dark skin are also at increased risk of vitamin D deficiency because the increased pigment in the skin (melanin) reduces penetration of UV rays and the production of vitamin D.
Obesity
Being overweight, particularly if you have a body mass index (BMI) of greater than 30 you are at increased risk of vitamin D deficiency. This is not because vitamin D production is decreased but because the subcutaneous fat decreases the release of vitamin D into the circulation. Even when vitamin D is taken orally through food or supplementation the amount of available vitamin D in the circulation is reduced in obese people.
Dietary sources of vitamin D
Very few foods contain significant amounts of vitamin D. The richest sources are oily fish such salmon, sardines, herring and mackerel. Other foods containing some vitamin D include milk, meat, eggs, cheese and fortified foods.
Most experts agree that it is very difficult to obtain sufficient vitamin D from foods alone and that sun exposure and/or supplementation is essential to prevent vitamin D deficiency.
