A new study suggests that seasonal variations in coeliac diagnoses might relate to the variations in virus infections in the course of a year. (Photo: Lucy Nicholson, Reuters, NTB Scanpix)

Birth seasons could impact risk of coeliac disease

Swedish children born in the spring ran a higher risk of getting gluten allergies by the age of two. The risk also rose the further south in Sweden the children lived.

Gluten is a hot item. Whether healthy persons should avoid gluten proteins is perhaps debatable, but persons with coeliac disease, also called a gluten allergy, must avoid glutens the rest of their lives.

Gluten proteins are found in grains such as wheat, barley and rye. The protein is thus present in all sorts of foods such as breads, pastries, pasta, many processed foods and snacks. People with the allergy have to be meticulous in reading lists of ingredients and watching out for what they can and cannot eat.

Despite new research about coeliac disease, scientists still don’t really know why some people develop this problem and others can eat loaves of bread and fork in plates of spaghetti without gastrointestinal discomfort. It is known that those who develop the disease share specific genes but these genes alone are not enough to trigger the allergy. 

This leads scientists to look for external causes. Environmental factors and virus infections are some of the major suspects.

Researchers at Sweden’s Umeå University have now investigated the connection between the time of year a person is born and the risk of developing coeliac disease during the first 15 years of life. They also looked at the variations of risks depending on where in Sweden people were born.

Winter children safest

The new study is extensive. The researchers analysed the diagnosis date and the birth months of 1.9 million Swedish children born from 1991 to 2009. 

The researchers got their information from national health registers. All children with coeliac disease had been diagnosed through intestinal biopsies.

They found that the risk of coeliac disease was higher among children born in the spring, summer and fall, compared with winter babies. The risk of coeliac disease was highest overall amongst children born in the spring. This concerned children who were diagnosed before age two. For children who were diagnosed from age two to 15, the risk was greatest among those born in the summer and autumn.

Furthermore, when the researchers divided up these persons in groups according to when they were born, they found that the risk was greatest for spring births in the years 1991 to 1996, from the summer to the fall among those born from 1997 to 2002, and in the fall for those born in the period 2003-2009. 

Professor Geir Aamodt at the Norwegian University of Life Sciences, suggests that this spread in the findings indicates that the conclusions should be taken with a grain of salt.

“This indicates a big variation in the data. This means that the results could be random findings and that there are no certain correlations between risk of coeliac disease and birthdates.

Geographic variations

The Swedish findings also uncovered differences in risks of coeliac disease depending on where in Sweden the kids lived. The further south in Sweden, the larger their risk of the intestinal disease.

Aamodt and some of his colleagues have researched geographical differences in instances of the gut disorders Crohn’s Disease and ulcerous colitis. These diseases involve inflammations of the mucous membranes of the gut and like coeliac disease their causes are something of a mystery. But it is known that particular genes are present in the patients of these diseases too.

“These geographic variations are observed for a number of autoimmune diseases, such as diabetes type 1 and inflammatory bowel disease. But here we actually see the opposite findings. We have seen that the risk of the disease is higher the further north we go, creating a so-called north-south gradient.”

“This has been seen, among others diseases, for Crohn’s and ulcerous colitis. Here in Norway too.”

Virus and vitamins

The researchers behind the study of a seasonal variation in coeliac disease diagnoses think there may be a link to variations in virus infections throughout the year and the introduction of foods containing glutens.

Children born in the spring are most often introduced to solid foods in the fall and winter. These are seasons for more virus infections such as flu and colds.

Vitamin D is also named as a possible explanation of seasonal variations. The body relies on sunlight to synthesise vitamin D. Children born in the autumn in Nordic countries can have a vitamin D deficiency, which the scientists think could add to these health risks. 

But these theories get eroded by the geographical data, where the risks rose the further south the Swedish kids lived. Further south in Sweden there is more winter daylight than further north.

Aamodt has also seen associations between climate and the risk of illness in his studies. He thinks that temperatures might have a role here.

“Getting lots of sunlight does not only provide you with vitamin D, but warmth as well. High temperatures might raise the diversity of benign bacteria in the gut system and thus promote disease resistance.”

The Swedish researchers have not gathered or factored in data about the vitamin D status of the Swedish children.

“This is a huge study covering a large cohort. But it is a register study, gleaning data about the individuals from national health registers. The researchers have information about ages, genders and diagnoses but not much more. There can be factors impacting the coeliac disease risk which the researchers are not seeing,” suggests Aamodt.

“Diet, for instance, affects both the activity of coeliac disease and foods we eat also vary to some extent along with seasons and geographical habitat.”

He points out that such observation studies generate hypotheses but are not as suited for drawing scientific conclusions.

“More research is needed on environmental factors and the risk of autoimmune disorders such as coeliac disease. It might also be interesting to look at all the autoimmune diseases combined and see whether there could be any common risk factors in play. We have big gaps in research here.”


Read the Norwegian version of this article at forskning.no

Translated by: Glenn Ostling

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