Dhaka, Oct. 5 -- As the days grow shorter and colder, doctors are warning that most people will not get enough vitamin D from sunlight alone -- and that the effects can be more serious than many realise.

Vitamin D is essential for healthy bones, muscles and immune function. Unlike most vitamins, it cannot be obtained in sufficient quantities through diet, and the body's main source is sunlight on the skin, reports The Independent.

In the UK, sunlight is too weak between October and March to trigger the chemical reaction that produces it.

"Even on a sunny day in the UK autumn and winter you just won't get enough vitamin D from the sun," says Dr Henrik Premasundaram, a GP at HCA Healthcare UK.

A deficiency can cause fatigue, bone pain a...