Scientists believe going out in the midday sun without sunscreen for 10-15 minutes is good for you, contrary to current advice.
Sun exposure triggers vitamin D production by the skin
Cancer Research UK says people should stay in the shade from 11am to 3pm to avoid damage from the strong rays.
But a team from the University of Manchester argues that a short burst of sunshine on unprotected skin at noon can maximise vitamin D production.
Enough vitamin D is essential for healthy teeth and bones.
Researchers have also suggested that vitamin D might protect against some cancers.
But Cancer Research UK said too much sun could cause cancer and advised people to protect themselves against sun damage.
However, Dr Ann Webb, who ran the Manchester study, said: "Our calculations have found that the best time to be out in the sun if you want to maximise vitamin D production and its benefits is midday.
Stay in the shade 11-3pm
Make sure you never burn
Always cover up
Remember to take extra care of children
Then use factor 15+ sunscreen
Source: Cancer Research UK
"This is when the sun is highest in the sky and is when there is more UVB radiation in the spectrum which triggers vitamin D production in the skin."
Cancer Research UK warns it is the same UVB radiation that causes sunburn, and some fair skins may burn in a very short time in the midday summer sun.
Using computer simulations based on global UV data, Dr Webb's team, working with colleagues from the Norwegian Institute of Air Research, estimated how long people should stay out in the sun this Bank Holiday to get a maximal dose of vitamin D, based on where they are in Europe:
- Edinburgh - 11 minutes
- Manchester, Leeds, Liverpool - 10 minutes
- London - 9 minutes
- Devon and Cornwall - 9 minutes
- Marseille - 7 minutes
- Madrid - 7 minutes
- Athens - 6.5 minutes
These times are based on full sun exposure at midday on Bank Holiday Monday with a cloudless sky for a fair-skinned person wearing a T-shirt and shorts or a skirt.
Dr Webb stressed that she did not want to encourage people to sunbathe for long periods.
"After a short period of unprotected exposure, you should cover up or put on sunscreen to avoid sunburn."
She pointed out that it was also possible to get plenty of vitamin D from the diet, by eating vitamin D rich foods such as sardines.
Sara Hiom, Head of Health Information at Cancer Research UK, said: "Our SunSmart campaign currently recommends finding shade between 11am and 3pm to protect people from burning, especially the fair-skinned.
"Our recommendations have been based on expert consensus and the scientific evidence available to date.
"However, Cancer Research UK will always consider any new evidence when reviewing our sun protection messages.
"If people expose their unprotected skin to strong sunshine, we would urge them not to burn, as does Dr Webb."