A very large British study involving 1.1 million middle-aged women without prior vascular disease has found, over nine or so years, those who performed strenuous physical activity two to three times a week were about 20% less likely to develop heart disease, strokes or blood clots, compared to participants who reported little or no activity. However, those who reported doing strenuous activity daily had higher risk compared to those who only engaged in moderate amounts of activity.
Armstrong, M. E. G., Green, J., Reeves, G. K., Beral, V., & Cairns, B. J. (2015). Frequent Physical Activity May Not Reduce Vascular Disease Risk as Much as Moderate Activity Large Prospective Study of Women in the United Kingdom. Circulation, 131(8), 721–729. http://doi.org/10.1161/CIRCULATIONAHA.114.010296