The cause of schizophrenia has long baffled doctors, but a tantalizing clue has emerged that some cases of the debilitating mental disorder are linked to having too little vitamin D during fetal development and early in life.
Researchers studying schizophrenia cases in Denmark have discovered that newborns with the lowest level of the sunshine vitamin in their blood at birth had about twice the risk of developing the disease when they became adults, compared to those with moderate amounts.
The finding suggests it may be possible to reduce the incidence of the illness by having babies and pregnant women either take the vitamin, or increase their exposure to sunshine, the natural way of making the nutrient.
"The study opens up the possibility that improving vitamin D levels in pregnant women and newborn babies could reduce the risk of later schizophrenia," observes John McGrath, director of the Queensland Centre for Mental Health Research, one of a team of Australian and Danish researchers who conducted the investigation.
A paper on the findings appeared earlier this week in Archives of General Psychiatry. The research is the first to link neonatal vitamin D levels and the brain disease.
Schizophrenia is a severe mental illness in which people often experience hallucinations and hear voices. It typically develops in young adults, around the age of 20, and causes a lifetime of symptoms that sometimes can be controlled through medications.
It's thought that the disease lies dormant until after puberty, when changes in the brain allow symptoms to break through and become apparent.
Researchers have long scratched their heads over why some people develop the disease, which affects an estimated one person out of 100 in Canada. Previous studies have found it's more common in children born to older fathers, for instance, as well as among those living in urban areas, and in non-white immigrants to northern latitude areas.
But one previously identified risk factor has hinted at an insufficiency of vitamin D: the time of year a child is born. Children with winter births, when mothers' vitamin D levels are typically low because of the lack of exposure to strong sunlight, have about a 10-per-cent higher risk of schizophrenia than those born at other times of the year. Fetuses depend entirely on their mothers for the nutrient.
For winter births, this seasonal fetal vitamin D famine occurs during the last stages of pregnancy, a time when brain development is very rapid and the lack of a key nutrient could have a major impact. The new research is an important breakthrough because it tracked actual vitamin D levels in children, rather than the inferred amounts from the season of birth.
Previous experiments by Dr. McGrath have found that pregnant rats deprived of vitamin D give birth to pups with altered brain development. One possible link to schizophrenia suspected by the researchers is that too little vitamin D before birth alters the brain's dopamine system, an important chemical factor influencing mood and other mental processes.
The research on newborns was based Denmark's vaunted Newborn Screening Biobank, which has collected dried blood samples from all children born in the country since 1981. Vitamin D levels in the blood were compared in 424 people, ranging in age from 16 to 29, who had developed schizophrenia and an equal number of so-called controls who had not. These comparisons found the excess risk among those with low levels.
A paradoxical finding in the research is that the babies with the highest amounts of vitamin D also had an elevated risk of the mental disease, at first glance suggesting that both too little or too much of the nutrient might be a bad thing when it comes to schizophrenia.
But Dr. McGrath played down this possibility and said there may be a subgroup of the population that has difficulty metabolizing vitamin D into the form used by cells, causing levels of the nutrient to build up in their blood. These individuals would consequently have cells experiencing shortages, while simultaneously having high blood levels awaiting to be converted.
Dr. McGrath said the possibility that there is a vitamin D resistant part of the population is "pure speculation," and needs to be confirmed by more research into genetic differences in the way people metabolize the nutrient.