International experts are calling for food in Scotland to be fortified with vitamin D, in an attempt to cut the large numbers of people who develop multiple sclerosis at sunshine-deprived northern latitudes.

MS levels in Scotland are some of the highest in the world, and many believe vitamin D deficiency, caused by lack of sunlight and poor weather which keeps people indoors, is partly to blame. For half the year, nobody living in Scotland gets enough UVB rays from the sun on their skin to make adequate amounts of vitamin D and many do not eat enough of the foods, such as oily fish, that contain it.

Professor George Ebers of the Nuffield Department of Clinical Neurosciences at Oxford University believes the evidence is now good enough to justify dosing the entire population with vitamin D. This month his team published evidence of a genetic link between a rare inability of the body to make vitamin D and MS.

It is a piece of strong scientific evidence to back up theories based on the high numbers of people with MS in sun-deprived locations – there are 10,000 with the disease in Scotland – and very low numbers in countries with year-round sunshine.

"Now the question is, can we finally persuade the public health authorities that they should supplement the population?" said Ebers.

The cause of vitamin D has been taken up by Shine on Scotland, a campaign launched by 13-year-old Ryan McLaughlin in response to his mother's diagnosis with MS. Kirsten McLaughlin is now very ill in hospital. The campaign is supported by the MS Society in Scotland, has involved a march on the Scottish parliament and resulted last year in an international summit in Glasgow involving scientists, campaigners and Scottish health secretary Nicola Sturgeon.

Ryan's father, Alan, said he and Ryan had another meeting with government officials on Wednesday where they urged food fortification.

"We still think that's the best way to go," he said. "We have started having talks with manufacturers about milk or fruit juice." They have persuaded Kellogg's to add extra vitamin D to their cereals.

Unfortunately, he says, the levels are still minimal, "but it sets a benchmark".

Scotland's chief medical officer Sir Harry Burns says there needs to be "broader scientific consensus" before change is considered. "It is important to remember that dietary supplements can have harmful as well as positive consequences and recommendations need to be made on the basis of evidential benefit in well conducted randomised studies in large populations.

"Mass medication of the Scottish population without such evidence would be considered irresponsible by the public health community," he said.

He wants to wait for the conclusions of a review of the evidence under way by the UK government's scientific advisory committee on nutrition – a process that will take until 2014. But Professor Ebers says that is too long. He fears a repeat of the folate story. There was strong scientific evidence in the 1980s – and suspicion earlier — that folic acid deficiency in pregnant women was a cause of neural tube defects in babies, causing death and conditions such as spina bifida.

It took decades for the public health authorities to agree that pregnant women and those seeking to become pregnant should be routinely prescribed folic acid tablets. But the harm occurs in the first four weeks of pregnancy, which means that even now, women who do not know they are pregnant will not be taking the supplement.

"I think that the neural tube defect story should not be reinvented here," said Ebers. "They should supplement the population as a way of guaranteeing that everyone gets it and that levels at key times are not deficient."

International experts met in Chicago earlier this month to look at the evidence for the link between vitamin D and MS and work out a way forward. Discussions centred on the evidence that public health bodies and governments would need to act, which could include a randomised trial, comparing the numbers of MS cases that develop among young people given regular high doses of vitamin D and among others who are not.

But a number of scientists feel strongly that there is no longer a need for more proof in Scotland.

"I'm convinced it is vitamin D in Scotland," said Bruce Hollis, professor of paediatrics and biochemistry at the Medical University of South Carolina. In 2004, he went there with Ebers to make the case for supplementation. A randomised trial, he says "is never going to happen". It would cost millions and there is no drug company to fund it in the expectation of making a profit because the vitamin is so cheap.

Hollis rejects the caution of some public health officials and academics. The Institute of Medicine in the US said there was no proven case that vitamin D supplementation was useful except in bone health.

"These guys haven't been studying it like I have for 30 years," said Hollis. He added that there were zero side-effects from taking vitamin D, even in the high doses that he and Ebers are advocating against MS and which people who are out in the sun a lot would get anyway.

"If you look at women who are chronically sun-exposed and athletic, sometimes their levels would exceed the 4,000 international units a day we are giving to pregnant women. This has been going on in humans since the beginning of time, until we moved away [from equatorial Africa] to northern latitudes."

Reinhold Vieth, professor of nutritional sciences at the University of Toronto in Canada, says that advising people to take vitamin supplements will not work. Food fortification is needed, he says, at higher levels than the small amounts already added to food in north America to combat rickets in the past.

"For example, if not for iodination (fortification) of table salt, many people would be walking around with goitre," he said.

"If the amount of iodine in table salt were as tiny in the context of reality, as even the fortification in North America is with vitamin D, then people would still be walking around with goitre.

"If people had to buy and consume supplements with iodine to prevent goitre, most people would not do it, and people would still be walking around with goitre.

"Goitre is so obvious, you jump at the chance to do something about it.

"Lack of vitamin D is not so obvious, so policy makers can hide behind the boogie man that they don't yet know enough about the potential risks. Government policymakers love doing nothing, and any reason to do nothing is good enough for them. "

Doug Brown, head of biomedical research at the MS Society, believes the Chicago meeting "really is a turning point in this research – which will translate into potential benefits for people with MS".

The scientists will publish a strategy in an international journal. "We believe the mounting evidence is now too important to ignore," said Brown.

The vital ingredient?

Vitamin D is vital to the absorption of calcium and phosphorus by the gut, which is why low levels can cause the bone disease rickets. In Victorian times, when rickets was rife among the poor, children suffered softening of the bones and ended up with bow legs because their diet was so bad, with little in the way of calcium from dairy products. In recent years rickets appears to have had a resurgence. The reason this time is a lack of vitamin D and there is speculation that children's indoor life, focused on computer games and TV, may be partly to blame.

The body synthesises its own vitamin D from sun exposure. In northern climes, where the sun is not strong enough in the winter and people are wrapped against the cold or mostly indoors, the body uses up stocks of vitamin D made in the summer. Some foods contain vitamin D, but they are not our prime source. It is in oily fish such as salmon and sardines, eggs, and foods like cereals to which it has been added.

People with darker skins are at greater risk of vitamin D deficiency and so are those who stay fully covered because of their religious beliefs. While over-exposure to the sun is harmful, all of us need perhaps as little as 10 to 15 minutes a day to maintain adequate vitamin D levels.