Everyone should consider taking vitamin D supplements in autumn and winter, public health advice in England and Wales says.
It comes as a government commissioned report sets theb recommended levels at 10 micrograms of the vitamin a day.
But officials are concerned this may not be achievable through diet alone, particularly when sunlight, which helps in vitamin D production, is scarce.
Low vitamin D levels can lead to brittle bones and rickets in children.
Top-ups
Limited amounts of the vitamin are found in foods such as oily fish, eggs and fortified cereals.
But, for most people, the bulk of their vitamin D is made from the action of sunlight on their skin.
And official estimates suggest one in five adults and one in six children in England may have low levels.
Now, an extensive review of the evidence, carried out by the Scientific Advisory Committee on Nutrition (SACN), suggests everyone over the age of one needs to consume 10 micrograms of vitamin D each day in order to protect bone and muscle health.
And public health officials say, in winter months, people should consider getting this from 10 microgram supplements, if their diet is unlikely to provide it.
Why is vitamin D important?
Its main function is to regulate the amount of calcium and phosphate in the body, which are vital for the growth and maintenance of healthy bones, teeth and muscles.
In extreme cases, low levels can lead to rickets in children - where the bones become soft and weak and misshapen as they continue to grow.
In adults, vitamin D deficiency can lead to osteomalacia - causing severe bone pain and muscle aches.
