The lack of sunlight in Sweden, combined with the use of sun protection creams and general precautions taken to avoid direct sun exposure is known to cause vitamin D deficiencies. Vitamin D deficiencies could be a contributing factor to the incidence of depression and some experts believe, autism.
Somalis living in Sweden have dubbed autism, "The Swedish disease," as it has become an increasingly common occurrence among Somali children that have moved to Sweden.
The incidence is far higher than for Somali children resident in Somalia, something which researches theorize may be related to differences in the amount of sunlight between Sweden and the east African country.
"Dark-skinned people demand significantly more sunlight to enable vitamin D to build up in their skin. The combination of clothing which covers the body and dark skin is a particularly problematic combination, especially for someone that doesn't eat fatty fish," write senior doctors Susanne Bejerot and Mats Humble in an opinion article published in the Dagens Nyheter newspaper.
The pair argue that a massive information campaign is needed in Sweden in order to highlight the risks of vitamin D deficiency - which affects half of Sweden's population.
In looking for explanations as to why autism in more prevalent among Somali children living in Sweden, Bejerot and Humble suggest that research should focus on the different environmental factors between Sweden and Somalia and also the factors between different immigrant groups living in Sweden.
"One factor could be just sunlight and the effect of sunlight. At our northern latitudes we are only exposed to sufficient sunlight to build up our vitamin D for a few short summer months which explains that around half of the Swedish population suffers from a vitamin D deficiency."
The western world has seen a dramatic increase in autism in recent years and Sweden has followed this trend. Around 1 percent of the Swedish population suffers from this neurological condition. In the US, the diagnosis of autism is increasing at a rate of 10-17 percent per year.
Researchers are struggling to explain the dramatic increase. Some focus on the incidence of mercury in vaccines or the the MMR triple vaccine given to young children. Others blame the sedentary habits of western children and modern food habits.
Another explanation may be that changes to how the condition is diagnosed lie behind the dramatic increase. Regardless, a more complex picture of the combination of genetic, environmental and social factors behind the condition is starting to emerge.
The doctors regret that it will take time for research to show the link between the illness and levels of vitamin D in Sweden's population which would support their contention that a general vitamin D supplement is needed.
"With current knowledge we can not rule out that Vitamin D deficiency is a strong factor behind the so-called autism epidemic. The connection can be researched scientifically but will take several years."
The National Board of Health and Welfare (Socialstyrelsen) has not issued any recommendations for how the widespread incidence of vitamin D deficiency should be treated and are unlikely to do so before 2012.
Bejerot and Humble explain that vitamin D is completely harmless in controlled doses and wonder therefore why the board is dragging its heels before developing "culturally sensitive" guidelines on the issue.