Australasian Science: Australia's authority on science since 1938

Age of Multiple Sclerosis Onset Linked to Latitude

A large international study has found that the age at which symptoms of multiple sclerosis (MS) first start is strongly linked to latitude.

The lead author of the study, Prof Bruce Taylor of The University of Tasmania’s Menzies Institute for Medical Research, said that each 10° increase in distance from the Equator was associated with a 10-month earlier onset of symptoms.

MS is thought to be caused by a complex interplay of genetic and environmental factors, including latitude and/or exposure to sunlight and vitamin D levels. Until now it was not clear whether latitude might also affect the age at which symptoms first start.

In an effort to find out, the research team drew on an international database of more than 22,000 MS patients from 52 centres in 21 countries in Europe, North and South America, Asia Minor, South Asia and Australia. Almost 16% were from Australia, including around 300 people with MS from Tasmania.

The average age at which symptoms first appeared was around 32. After taking account of potentially influential factors it emerged that each 10° increase in latitude was associated with a 10-month earlier start of symptoms, with those furthest from the Equator starting their symptoms almost 2 years earlier than those closest to the Equator.

A similar pattern emerged for exposure to ultraviolet B sunlight, which stimulates vitamin D production in the skin. People exposed to the smallest dose of UVB during the winter months showed symptoms 2 years ahead of those who received the largest dose.

Consistent with previous work, those with the primary progressive form of MS had a significantly later age of onset – around 9 years later.

In common with data on the incidence and prevalence of MS, nearly three-quarters of the participants were women, and 91.5% had the relapsing–remitting type of MS, which typically starts earlier than the progressive type.

The research was published in the Journal of Neurology Neurosurgery & Psychiatry.