One of Britain’s leading scientists has urged people to take vitamin D supplements, particularly children, who spend an hour less outside than they did 10 years ago.

The geneticist Steve Jones told the Hay literary festival in Wales the health case for taking them was now overwhelming. “I never thought I would be a person who would take vitamin supplements, I always thought it was absolute nonsense, it’s homeopathy. I now take vitamin D every day,” he said.

“Today, because I knew the sun wasn’t going to shine, I took an extra one.

“Children today spend an hour a day less outside than they did 10 years ago. That’s the smartphone and the tablet situation. Scottish children spend less time in the sun than any other children in the world.”

He said the bone disease rickets, which doctors thought they had eliminated from Britain in the 1950s, was a real issue today. “Rickets is coming back and rickets is coming back at some speed. It is coming back because of a shift in human behaviour which we never thought would happen,” he said.

Jones said the benefits of sunshine and vitamin D could be felt across a range of health areas including obesity, mood and blood pressure. He cited multiple sclerosis, which is most common in northern Canada and almost unheard of in tropical countries. In the UK, levels are higher in Scotland than England.

Scotland gets the least sunshine in the UK and Scottish men have a life expectancy two years less than men in England and Wales, he said. “Scotland is still the sick man of Europe. The Scots are the palest people in the world … and that’s because their entire body systems are crying out for vitamin D.”

Jones is professor of genetics at University College London and is considered one of the finest science communicators of his generation. He was in Hay talking about his new book, Here Comes the Sun.

Jones told the audience that vitamin D had many unexpected effects on the body, including the immune system. “It can help tackle infectious disease, it changes mood, if you have a shortage you’re more likely to get kidney disease … it is really, really important stuff. The evidence that the shortage of sunlight has drastic effects on health is overwhelming.”

The sun also lowers your blood pressure. “If you lie out on the beach in your bikini, or without anything on, for an hour you will drop your blood pressure by about 10 points, because it relaxes your blood vessels. So get out in the sun while we still can.”

Jones acknowledged that too much sun can cause skin cancer, a discovery made in the 1930s during research on the health of US Navy sailors. It was also discovered that they had lower levels of other diseases because of their greater exposure to the sun. “That was forgotten more or less, but it’s now being discovered in spades.”