A study published in the BMJ Open journal shows that even moderate coffee consumption during pregnancy, one to two cups per day, is related to a risk of overweight or obesity in school age children. It has not been clearly shown if caffeine is the direct cause of the overweight, but the relationship, alone, has caused researchers to encourage increased caution.

"There may be good cause to increase the restriction of the recommended maximum of three cups of coffee per day. Caffeine is not a medicine that needs to be consumed," says Verena Sengpiel, Associate Professor in obstetrics and gynecology at Sahlgrenska Academy, Sweden, and specialist physician at the Department of Obstetrics and Gynecology at Sahlgrenska University Hospital.

Researchers at Sahlgrenska Academy, in collaboration with the Norwegian Institute of Public Health, studied information on 50 943 pregnant women, in one of the world's largest health surveys of pregnant women, the Norwegian Mother and Child Cohort Study (MoBa).

The results show that children born to mothers who consumed caffeine during pregnancy are at greater risk of being overweight at preschool and school ages. Children were followed until eight years of age. Being overweight in childhood has previously been linked to increased risk of cardiovascular disease and Type 2 diabetes later in life.

For example, at age five, the share of children who were overweight or obese was five percent greater in the group whose mothers had the highest caffeine consumption in the study, compared to those whose mothers had the lowest caffeine consumption.

The association between caffeine consumption during pregnancy and the risk of excess growth and overweight or obesity in children could also be seen in women who had followed the recommended amount for pregnant women. According to the National Food Agency, Sweden, pregnant women should not consume more than 300 milligrams of caffeine per day, which is equivalent to three cups of coffee (1.5 dl each) or six mugs of black tea (2 dl each).

The results of the current study are supported by at least two other studies; however, these included significantly fewer subjects and fewer sources of caffeine. This time, coffee, tea, chocolate, energy drinks and other sources were included.

"In the Nordic countries, coffee is the primary source, while, women in, for example, England receive the greatest amount of caffeine from black tea. If you look at mothers in the younger age group, it comes from energy drinks. We included different sources in the study and found a similar association between caffeine consumption from these different sources and children's growth," says Verena Sengpiel.

In general, the gestational environment is viewed as being important in the turning off and on of genes and metabolic programming for the duration of life. Previous animal studies, where embryos were exposed to caffeine in the womb, were also followed by excess growth and cardiometabolic disease in the offspring.

"Even if more studies are needed before we can say what this finding really means, caffeine is a substance that you can choose to reduce consumption of or completely refrain from during pregnancy," notes Verena Sengpiel.