Experts have warned the highly acclaimed "Slip Slop Slap" campaign may have been taken too far by a nation terrified of skin cancer.
Melbourne Pathology director Ken Sikaris, who oversees 1500 vitamin D tests a week, said the rate of deficiencies was "mind-boggling".
Dr Sikaris said people had become overly protective when it came to sunshine, pointing out that Slip Slop Slap "is a pendulum and it's gone a bit too far".
"There's a balance … you need sunlight but don't go out in the middle of the day for an hour when the UV is most harmful," he said.
Sydney endocrinologist Terry Diamond said under current recommendations 20 to 30 per cent of the population had deficient or insufficient levels of vitamin D.
But he said there was emerging evidence the optimal level to maintain bone health should be 40 per cent higher than national guidelines.
"That would mean 60 to 70 per cent of the population have deficient or insufficient levels of vitamin D," Professor Diamond, of St George Hospital, said.
Vitamin D is converted from cholesterol in the blood by sunlight and helps increase calcium absorption in the intestine, which builds stronger bones. Australians receive about 90percent of their intake from sunlight production, a function that is hindered by wearing sunscreen.
But in the past six years, average daily presentations to Australian hospitals with broken bones due to osteoporosis have risen from 177 to 262 - costing the medical system $1.9 billion a year.
Osteoporosis Australia head Peter Ebeling said the situation had become "very serious".
"I think we need to do everything we can to prevent the number of broken bones that are occurring," he said. "If people think about getting out into the sun for a little time when it's safe during the summer months … that would be good. If they're not able to do that I think vitamin D supplements are very important." Professor Ebeling said emerging research had linked vitamin D deficiencies to colon, breast and prostate cancer, diabetes, multiple sclerosis and other diseases.
"I think a lot of us have been worried about it for a long time but have just realised how widespread it is over the last five to 10 years," he said. "Like most people, we wouldn't have thought it would be very widespread in Australia but it seems that it is." Australia remains the skin cancer capital of the world, with more than 9500 cases of melanoma diagnosed every year and 1600 deaths.