Drinking three cups of tea a day during pregnancy increases the risk of having overweight children, according to a study of more than 50,000 mothers.
It found pregnant women who consumed more than 200mg a day of caffeine were more likely to have children that are overweight at preschool and school ages.
The study, which was carried out by researchers at Sahlgrenska Academy in Sweden in collaboration with the Norwegian Institute of Public Health, tracked the weight of children up to the age of eight and was one of the world's largest health surveys of pregnant women.
It has prompted Swedish researchers to encourage increased caution when consuming caffeine during a pregnancy.
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"Caffeine is a substance that you can choose to reduce consumption of, or completely refrain from during pregnancy," said Verena Sengpiel, associate professor in obstetrics and gynecology at Sahlgrenska Academy.
Researchers found that when the children were five years old the number who were overweight or obese was five percent greater in the group whose mothers had the highest caffeine consumption, compared to those whose mothers had the lowest caffeine consumption.
High levels of caffeine can also be found in drinks and chocolate.
Sengpiel explained: "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".
Caffeine is the world's most widely consumed central nervous system stimulant. It occurs naturally or is added to foods and beverages, with coffee and tea as the most common and major sources. During pregnancy, elimination of caffeine is prolonged and it rapidly passes all biological membranes, including the blood-brain and placenta barriers, resulting in exposure of the foetus.