In the most wide-ranging survey of the nutrient to date, researchers found that levels of the vitamin varied wildly between seasons. Deficiency rates soared to almost 50 per cent for those living in Victoria and the ACT during winter.

Specialists say this is a warning that people are limiting their exposure to the sun by spending too much time indoors, thereby increasing their risk of poor bone health and chronic disease due to poor levels of the vitamin.

''It's a real problem which alerts the population that we shouldn't dismiss it,'' Rebecca Mason, a professor of physiology at the University of Sydney's Bosch Institute, said.

She said Australians needed at least 10 minutes of exposure to the sun on the arms during mid-morning or afternoon in summer to receive adequate vitamin D, which is absorbed through the sun's ultraviolet-B rays.

''We are spending far too much time indoors watching television and using technology,'' Professor Mason said. ''We're just not getting out there enough - with or without sunscreen.''

The survey also found that about one in 20 people took supplements in 2011-12. The majority were women aged over 54.

Surprisingly, about one in three young adults aged 18 to 34 were deficient, double the number of people aged between 65 and 74.

Although most of those surveyed were mildly deficient in vitamin D, more than 1.1 million people had moderate to severe deficiency.

But Australian Medical Association NSW vice-president Saxon Smith said historically people lacked the sunshine hormone, and low measures did not necessarily have negative health implications.

For people with renal failure or brittle bones, taking supplements is important, he said, but if ''healthy young Australians are measured during the middle of winter, then the results could be inconsequential''.

Dr Smith said estimates by the Royal College of Pathologists of Australasia showed that at least half the 4 million tests for vitamin D deficiency taken each year were ''unnecessary''.

It recommended that testing be limited to people at high risk of deficiency, including those with chronic kidney failure or strong risk factors, such as having very dark skin.

Recent studies have questioned the role of the vitamin in preventing chronic disease. One study, published in The Lancet, said taking supplements could be a waste of money and should be avoided.

Professor Mason said while there was ''overwhelming'' evidence that adequate vitamin D with calcium was important in reducing falls and fractures, as well as in lowering mortality, it was unclear if low levels were a marker of poor health.

Lead researcher on the Sun Exposure and Vitamin D Supplementation Study, Robyn Lucas, said high levels of deficiency confirmed that sedentary, indoor lifestyles were preventing many Australians from receiving sufficient sun exposure.

The year-long study involving 1000 participants will analyse the levels of sun exposure in managing vitamin D levels and how to balance getting sufficient sunlight without risking sunburn and skin cancer.

A participant in the study, Antonia Lehn, 58, said she was ‘‘astounded’’ to discover she was mildly deficient two years ago.

"I was really surprised. I do have an office job but I’ve always been an outdoors person and do a lot of bushwalking and running. I thought I’d be the last person with a deficiency," she said.