Campaigns on the dangers of too much sun have been very successful
Worries over skin cancer mean that some people are shunning the sun altogether - which could endanger their health, a poll has found.
The National Osteoporosis Society (NOS) says lack of vitamin D - part-made by being in the sun - could raise the chances of brittle bone disease.
It advised having lunch outside, gardening or hanging out the washing.
A Cancer Research UK spokesman agreed, but said enough vitamin D could be made long before the first signs of sunburn.
Skin cancer rates have soared in recent years, and health campaigners increasingly urge people to limit the amount of time they spend in direct sunlight without the protection of sunscreen or clothing.
However, the NOS said its survey of more than 2,600 people in June revealed that many believe there is no such thing as safe sun exposure.
Three-quarters of those questioned said that sunscreen should always be applied before going out in the sun.
However, the NOS said that not getting at least 15 to 20 minutes of sunlight on the skin every day could be harmful.
Light falling on the skin produces vitamin D, which is important for bone strength, and studies suggest that low levels of this could raise the risk of osteoporosis, which affects half of all women and a fifth of men over the age of 50.
Professor Roger Francis, from the NOS Medical Board, said its finding showed the success of public health messages on skin cancer.
"We are not advocating spending lengthy periods in the sun, as too much sun causes skin ageing and melanoma.
"Furthermore, staying in the sun too long means that the body breaks down surplus vitamin D shortly after it is produced.
"Lying on the beach for two weeks will not top up levels for the rest of the year."
He urged people to get out into the light every day - even during cloudy days - to get enough vitamin D to last through the winter.
Simply sitting by a closed window or in a conservatory was not enough, he said, as this did not produce vitamin D.
Caroline Cerny, from Cancer Research UK, which runs its SunSmart campaign to warn people about skin cancer, said the key was a sensible approach.
"The amount of time in the sun required to make enough vitamin D changes from person to person and depends on things like skin type, time of day, time of year, and where you are in the world .
"We all need a bit of sunshine in our lives, but it's important to remember that the amount of sun needed to make enough vitamin D is always less than the amounts that cause reddening of the skin or sunburn."