Researchers found that birth weight is linked to heart disease in adults due to risk genes shared by mothers and their children.

Most previous studies show that people born small are at increased risk of developing hypertension and heart disease in adulthood.

The biological cause of this phenomenon has been debated for decades, but there is no definitive research evidence. One popular theory is that inadequate nutritional intake during pregnancy affects the developing foetus' metabolism, predisposing it to cardiovascular disease during periods of overnutrition.

The findings, published in the journal Communications Biology, showed that maternal genetic factors that influence the growth of the developing foetus have a birth weight-independent effect on the child's subsequent risk of heart disease.

However, it appears that these genes only play a role in disease risk when they are passed on to the child, said the researchers from the University of Helsinki in Finland.

"Certain maternal genes influence the growth conditions of the child in the womb and consequently the birth weight of the child. The child in turn inherits a copy of these genes from the mother," said Jaakko Leinonen, a Postdoctoral Researcher at the Institute for Molecular Medicine Finland (FIMM) at the University of Helsinki.

"When we studied the impact of these birth weight genes on children's morbidity later in life, we found that small changes in the baby's growth before birth due to the mother are unlikely to have a major impact on the child's risk of developing the disease as an adult. Instead, it seems that a child's own genes play a much more important role in determining his or her future health risks," Leinonen added.

The new research results were obtained by looking at the genetic data of more than 36,000 such mother-child pairs.

According to the researchers, previous genetic studies have produced partly different results because they have not been able to distinguish between the genetic effects of mother and child.

"Our research method, which uses genetic data from both mothers and their children at the same time, has proven to be a very effective way to find out how maternal health and the conditions of the baby in the womb can affect the health of the child," said Dr Taru Tukiainen, who led the study.

More research is needed to find out how being born significantly underweight or other significant changes in birth weight affect the risk of disease in adulthood.