Almost six out of ten Australians have insufficient vitamin D and should seek advice from their GP.
So says Professor Michael Holick, one of the world's most influential vitamin D experts, who is visiting Australia to highlight the hidden epidemic of deficiency.
Most people know vitamin D is important for bone health but the Boston professor of medicine, physiology and biophysics says other risks include pre-eclampsia in pregnancy as well as heart disease, type 2 diabetes and infectious diseases.
"The message is clear. Vitamin D plays a critical role in the processes of holistic preventative health," the author of The Vitamin D Solution told the BioCeuticals Research Symposium in Sydney.
He says it is not necessary for everyone to have a blood test, but people should discuss their circumstances with their GP.
Obese people, those with inflammatory bowel disease or those on certain medications could be at higher risk and should be tested.
Vitamin D comes from food, sun and supplements.
However, sun exposure is problematic because of skin cancer, and food does not provide enough and is rarely fortified.
Prof Holick says SPF 30 sunscreen reduces people's ability to produce vitamin D by about 95 per cent.
"If you want to go out in the sun, always protect your face," he says.
Limited exposure of other parts of the body mid-morning and mid-afternoon a few times each week is beneficial.
Prof Holick has developed an app to help people measure vitamin D production and warn about too much sun exposure.
"But the best way to guarantee vitamin D sufficiency is to take a supplement, even in the summer."
He believes general winter aches and pains and stiff muscles are symptoms of deficiency.
Professor Holick has conducted a small study that indicates vitamin D affects 291 genes.
He hopes a larger study will prove vitamin D levels affect the genes associated with several chronic diseases.
"For the first time, this study shows direct evidence that improving vitamin D levels plays a large role in improving immunity and lowering the risk for many diseases," Prof Holick says. AAP
WHY WE NEED VITAMIN D
• Bone health, absorption of calcium from the intestine
• Important for growth and maintenance of a strong skeleton
• Helps control calcium levels in the blood and helps maintain muscle strength
HOW MUCH SUN? (Consult GP)
Warning: Balance sun exposure with the need to avoid skin damage.
Summer, moderately fair skin
• 5-10 minutes, most days
• Arms or legs exposed
• Mid-morning or mid-afternoon (Avoid peak UV times)
Summer, darker skin
• 15-60 minutes, most days (depends on geographical area and skin type)
• Mid-morning or mid-afternoon
Winter, moderately fair skin
• 7-30 minutes
Winter, darker skin
• 20 minutes to 3 hours (depends on geographical area and skin type)
Housebound elderly people, naturally darker skinned people, sun avoiders, indoor workers
Source: Osteoporosis Australia