Unnecessary testing for levels of vitamin D is costing Australia's healthcare system about $87 million a year and contributing to the sector's carbon footprint, according to Australian researchers.

The researchers found in 2020, more than 4.4 million vitamin D tests were funded by Medicare, enough tests for one in every six Australians.

Of those tests, 76.5 per cent, or some 3.4 million, were of no benefit to the patient or healthcare sector, according to the study, led by the University of Sydney and published in BMJ Open.

The spike in testing in 2020 occurred despite a drop off in requests between March and May, coinciding with COVID-19 restrictions.

The number of tests requested was up 11.8 per cent from the average in 2018 to 2019, according to data collected through Medicare.

The emissions generated from the tests was between 28,000kgs to 48,000kgs of carbon dioxide.

Healthcare is already a significant carbon emitter - in 36 major countries it is responsible for 4.4 per cent of annual emissions - in Australia, the healthcare sector is responsible for seven per cent of emissions.

Previous research indicated that up to 76.5 per cent of vitamin D tests were carried out on people who did not meet criteria for testing, and high rates of testing occurs in people with no risk of deficiency, the study's leading author Matilde Breth-Petersen from the University of Sydney's School of Public Health said.

"We need to reduce low-value care such as over-testing and over treatment," Ms Breth-Petersen said.

Low-value care are services of limited or no benefit to patients, but still coming with a risk or cost to the patient or health system. These services make up about 30 per cent of the system.

The findings presented an opportunity for the healthcare sector to cut waste and reduce its carbon footprint, according to senior author Alexandra Barratt from the University of Sydney's Faculty of Medicine and Health.