The impact of HRT on cardiovascular morbidity is a subject of much controversy in the medical literature. The reduced risk of cardiovascular diseases associated with HRT, reported in observational studies, has not been subsequently confirmed in randomized clinical trials. The increased risk of cardiovascular disease in the WHI was not statistically significant, and only found in the oldest women, and those who started HRT late after menopause began.  The increase in risks of coronary heart disease in the treatment arm of the study varied according to age and years since onset of menopause. Women aged 50 to 59 using HRT showed a trend towards lower risk of coronary heart disease,  as did women who were within five years of the onset of menopause.