Dr Debbie Lawlor and colleagues in the Department of Social Medicine, analysed data from two UK Department of Health and British Heart Foundation sponsored studies of 4,286 women and 4,252 men aged 60 to 79.
They found that coronary heart disease (CHD) risk was lowest for women and men who had two children compared to those whose families were larger. Among women with more than two children, risk for CHD increased by 30 percent with each additional child. For men with more than two children, the risk increased by 12 percent for each additional child.
Obesity was more common among parents of large families. Mothers with more than two children were also more likely to have evidence of insulin resistance with low levels of high density lipoprotein (the 'good' cholesterol), raised triglycerides, raised blood sugar and diabetes. These risk factors increased with the number of children in the family.
Adjusting for obesity and other risk factors weakened the association between number of children and CHD risk, particularly in the case of fathers. However, a link still remained among mothers.
Dr Lawlor said: "Parents of large families tend to be poorer and also have less favourable lifestyles which explains some of their increased CHD risk.
"However, different results for fathers and mothers suggest that multiple pregnancies also have a specific adverse metabolic effect on women resulting in insulin resistance - an important risk factor for CHD.
"These results reinforce the need to encourage mothers and fathers of several children to maintain a healthy weight and lifestyle which may reduce their chances of developing obesity and CHD in later life.
"Careful screening and control of metabolic abnormalities during pregnancy should also be undertaken in women receiving antenatal care, particularly among women who have had a number of earlier pregnancies."
Is the association between parity and coronary heart disease due to biological effects of pregnancy or adverse lifestyle risk factors associated with childrearing? Findings from the British Women's Heart and Health Study and the British Regional Heart Study by Dr Debbie A Lawlor, MPH.; Mr Jonathan R. Emberson, MSc.; Professor Shah Ebrahim, DM.; Professor Peter Whincup, PhD,; Dr Goya Wannamethee, PhD.; Ms Mary Walker MA.; and Professor George Davey Smith, DSc