“Cardio,” as the name implies, is excellent for the health of your heart. Or is it? The idea is that cardiovascular exercise improves HDL (good) cholesterol, blood pressure, and triglyceride levels as well as insulin sensitivity. But is there a risk associated with cardio?

A study by Schnohr in 2015, found a U-shaped association between all-cause mortality (death from any cause) and the dose of jogging. Lower mortality was associated with light and moderate joggers, and higher mortality was associated with strenuous joggers. The strenuous joggers were found to have the same mortality rate as the sedentary group. (1,098 healthy joggers and 3,950 healthy nonjoggers followed over 2 years). The lowest mortality was associated with 1-2.4 hours of jogging per week, 2-3 times per week at a slow to average pace.

For those statistically minded:

1 to 2.4 hours of jogging per week was associated with the lowest mortality (multivariable hazard ratio [HR]: 0.29; 95% confidence interval [CI]: 0.11 to 0.80). The optimal frequency of jogging was 2 to 3 times per week (HR: 0.32; 95% CI: 0.15 to 0.69) or ≤1 time per week (HR: 0.29; 95% CI: 0.12 to 0.72). The optimal pace was slow (HR: 0.51; 95% CI: 0.24 to 1.10) or average (HR: 0.38; 95% CI: 0.22 to 0.66).

A systematic review by Li in 2018 showed that atrial fibrillation was significantly higher in athletes compared to the general population. Arterial fibrillation is an abnormal and serious heart rhythm characterized by the rapid and irregular beating of the atrial chambers of the heart. The review included nine studies with 2308 athletes and 6593 control subjects. Their findings showed the risk of atrial fibrillation is significantly higher in athletes than in the general population, especially among men and participants aged <60.

For those who are statistically minded:

Atrial fibrillation was higher in athletes than in the general population (OR = 2.34, 95% CI = 1.04-5.28). With a significantly increased risk in men (OR = 4.03, 95% CI = 1.73-9.42) and participants with mean age <60 (OR = 3.24, 95% CI = 1.23-8.55). Also, a significantly increased risk in participants who participate in a single type of sport (OR = 3.97, 95% CI = 1.16-13.62).

So, before you start training for that ultramarathon, keep in mind that research has shown that even with aerobic activity, moderation might be a rule of thumb.

• Li X, Cui S, Xuan D, Xuan C, Xu D. Atrial fibrillation in athletes and general population: A systematic review and meta-analysis. Med (United States). 2018;97(49). doi:10.1097/MD.0000000000013405

• Schnohr P, O’Keefe JH, Marott JL, Lange P, Jensen GB. Dose of jogging and long-term mortality: The Copenhagen City heart study. J Am Coll Cardiol. 2015;65(5):411-419. doi:10.1016/j.jacc.2014.11.023

• Abdulla J, Nielsen JR. Is the risk of atrial fibrillation higher in athletes than in the general population? A systematic review and meta-analysis. Europace. 2009;11(9):1156-1159. doi:10.1093/europace/eup197

• O’Keefe JH, Patil HR, Lavie CJ, Magalski A, Vogel R a., McCullough P a. Potential adverse cardiovascular effects from excessive endurance exercise. Mayo Clin Proc. 2012;87(6):587-595.