Having type 2 diabetes in the family more than doubles a woman's own risk of developing the disease, new research shows.
But the fact that fat - and certain dietary habits - also run in families accounts for a "substantial part" of this increased risk, Dr Rob van Dam of the Harvard School of Public Health in Boston and his colleagues found.
Having a close relative with type 2 diabetes - the kind closely linked to obesity - is a key risk factor for the disease, but known gene variants that increase diabetes risk only explain part of this relationship.
To investigate whether excess weight and lifestyle factors might also be involved, van Dam and his team looked at 73 227 women participating in the Nurses' Health Study. Over the course of 20 years, 5 101 developed type 2 diabetes, they report in the journal Diabetes Care.
Risk boosted more than two-fold
Having at least one parent or sibling with type 2 diabetes boosted the risk of developing the disease more than two-fold, the researchers found.
Women with a family history of diabetes were also more likely to be overweight, as were their family members, and this accounted for about 20%of the link between family history and diabetes risk.
And certain dietary habits shared by women and their relatives - specifically, drinking alcohol, eating red meat, and consuming sugar-sweetened beverages - also helped explain the association between family history and diabetes risk. The influence was smaller, though; alcohol accounted for 5% of the link, red meat 1%, and sugary drinks 3%.
The new findings, coupled with recent studies on diabetes-associated gene variants, van Dam and his team say, "suggest that most of the association between family history of diabetes and diabetes risk remains unexplained". - (Reuters Health, January 2010)