In the past decade, the number of Australians deficient in a crucial nutrient has risen as we increasingly shun the sun and shut ourselves away behind desks and digital screens.

Research shows up to a third of the nation may lack vitamin D, thereby increasing our risk of heart disease, diabetes, weaker bones, low mood and contracting the seasonal flu.

The elderly, pregnant and breastfeeding women, those with darker skin, veiled women and those in southern states may be the most deficient – with the problem increasing as the darker winter months encroach.

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“Because we all work longer hours and are less active and less outdoors, all of us are seeing a lot less sunlight,” said Osteopathy Australia spokesperson Claire Richardson.

Sunlight is the main way our bodies create the vitamin, and our growing deficiency is “very, very attributable” to our seeing less of it, Ms Richardson said.

“A lot of people I treat leave for work at 7 o’clock in the morning when it’s still dark and get home at 8 o’clock at night and they eat their lunch at their desks and they sit in a cubicle.

“The scary thing is, too, that we’re starting to have quite a high prevalence of vitamin D deficiency in adolescents, which is worrying.”

Dermatologist Dr Michael Freeman confirmed the deficiency is a “growing problem”.

The type sunlight of sunlight necessary for the vitamin’s production in the body is “really only available between 10am and 2pm”, Dr Freeman said — a time when many of us are indoors.

But be wary of canned sunlight

Unlike other vitamins, which can be flushed away in urine if we take too much, vitamin D builds up in the body.

This makes its pill form somewhat dangerous, as those who take it can be tempted to consume more than the recommended dose.

Super-dosing may cause toxic substances to leak from the blood into the brain, increasing the risk of degenerative brain conditions, a team of scientists at Curtin University reported in April in prestigious journal PLOS ONE.

The health benefits of the vitamin are “undeniable”, the study’s lead researcher confirmed, but it is false and potentially harmful to presume “a little but more gives us additional benefits”, he said.

“The benefits of vitamin D and the physiological importance of it is not something we are debating. It’s critically important for bone health and skin health and brain health,” said Curtin University health science expert Professor John Mamo.

“But if your levels are quite normal, then don’t take additional vitamin D.”

Even with pill supplements, sun exposure is still important, as without it our bodies can find it “very difficult” to absorb the nutrient, said Ms Richardson.

“You really need to kickstart that process by getting sunlight,” she said.

“Unfortunately, medicine is not always key to solving this problem.”

How to safely get enough vitamin D