New research has shown that being overweight in childhood and early adulthood raises the risk of developing blood clots in later years.

The University of Gothenburg study studied 37,000 men, looking at their early body mass index (BMI) and any blood clots that developed as they got older.

First author Lina Lilja, a doctoral student at the time of the study and now a senior physician in child health care, said: “Our study shows that both overweight in childhood and overweight in young adulthood increase the risk of venous blood clots later in life. The latter, overweight when the men were young adults, proved to be a more influential factor than overweight when they were children.”

While most blood clots, which usually occur in the legs, are not dangerous, they can be life-threatening if they travel to the lungs and a pulmonary embolism develops.

The link between obesity and blood clots is already well known but what has been less clear is whether a higher BMI in childhood influences the risk.

The researchers examined the data of a large group of men in Sweden who were born between 1945 and 1961. They established BMI data by looking at school records at age 8 and Armed Forces medical examinations at age 20. They then looked at blood clot data on the men up to an average age of 62.

The team found that BMI at both age 8 and age 20 can be linked to blood clots independently of each other.

As adults, it was found that two groups were more at risk – those who had been overweight both as a child and in early adulthood, and those with a normal weight in childhood but who became overweight in early adulthood.

In addition, it was found that carrying excess weight in both childhood and early adulthood increased a person’s risk of arterial thrombi, those clots which are the result of constricted blood vessels with fatty deposits. The team noted however, that more research is needed in this area as they only found a small number of cases.

One of the study’s senior authors, associate professor Jenny Kindblom, said: “Obesity and overweight during puberty seem to have a marked impact on a person’s future risks of venous thrombi.”

The study has been published in the Journal of Internal Medicine.

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