Whether or not wearing sunscreen prevents healthy vitamin D production will be examined in a major new study in Australia.
The first ever large-scale trial is looking for about 500 volunteers to investigate how applying SPF 50+ sunscreen affects the hormone largely generated in the skin through sun exposure.
"Lots of people are confused about how sunscreen will affect their vitamin D levels, and that causes them to either avoid sunscreen or spend too much time outdoors to try to get that balance," lead researcher Professor Rachel Neale says.
"The Sun-D Trial will provide evidence-based advice so we can clear up confusion in the community and the medical profession, arming people with the right information to enjoy the sun safely."
Participants in the eastern states are being encouraged to sign up, and researchers are keen to hear from those in Victoria and Tasmania where vitamin D deficiency is at its highest.
"Residents in these states are still told to wear sunscreen on any day where the UV index is forecast to reach or exceed three - that's actually most of the year," Prof Neale said.
"We want to make sure this advice is not causing vitamin D deficiency in these states, so we really urge people from Victoria and Tasmania to sign up."
Australia has the world's highest rate of skin cancer with more than 15,000 people diagnosed with melanoma each year, and sunscreen is vital to reduce the risk, Prof Neale says.
Participants must be aged between 18 and 70, have fair or olive skin and not be taking more than 10 micrograms of vitamin D supplements each day.
They will randomly be sorted into two groups; one will be given free sunscreen to apply every day, while the other will continue with their usual sun protection behaviour.
The study is being run by Brisbane's QIMR Berghofer Medical Research Institute.