Though the headline may sound like an obvious conclusion - we all know better physical fitness leads to better health outcomes - a new study published in JAMA Internal Medicine examines the role of cardiorespiratory fitness and its changes in young adulthood on long-term cardiovascular outcomes; previous research has only investigated this link in older adults.
"Most large studies of CRF [cardiorespiratory fitness] focus on middle-aged and older adults, demonstrating that fitness at a single point in time is associated with risk," write the authors, who are led by Dr. Joao A.C. Lima, of Johns Hopkins Medical School in Baltimore, MD.
As such, Dr. Lima and colleagues wanted to investigate baseline CRF and changes in young adults in relation to future cardiovascular disease (CVD).
They did this by assessing participants from the Coronary Artery Risk Development in Young Adults (CARDIA) study, which included 4,872 adults in the US aged 18-30 years.
Every 43 seconds in the US, someone has a heart attack, and every minute, someone dies from a heart disease-related event. Because heart disease is the leading cause of death for both men and women in the US, mitigating cardiovascular risks is a major public health priority.
Fitness reductions linked to 21% increased risk of death
As part of the study, participants underwent treadmill exercise testing at baseline, which was from March 1985-June 1986. Then, 7 years later, a further 2,472 participants had a second treadmill test.
The median follow-up time was 27 years, at which point, the participants were assessed for obesity, left ventricular heart mass and strain - which is a measure of heart muscle contraction strength - coronary artery calcification (CAC) and CVD.
- Each year in the US, 1 in 4 deaths are a result of heart disease
- Key risk factors include: high blood pressure, high LDL cholesterol and smoking
- Coronary heart disease is the most common type of heart disease.
Of the 4,872 participants, 5.6% died during follow-up, and 4% experienced CVD events. Of the 273 deaths, 200 were not cardiovascular related, and 22.5% of the deaths were related to cancer.
Additionally, out of 3,067 of the participants, 28.3% had any CAC by year 25, and out of 3,001 participants, 10.8% had a thickening of the heart muscle.
The treadmill tests in the study involved as many as nine 2-minute tests of gradually increasing difficulty, and the researchers say their results show that each additional minute of baseline treadmill test duration was linked with a 15% lower risk of death and a 12% lower CVD risk.
Furthermore, each 1-minute increase was linked with reduced left ventricular mass and better strain.
When the researchers conducted a second treadmill assessment at 7 years, they found that a 1-minute reduction in fitness by year 7 was linked with a 21% increased risk of death and a 20% increased risk of CVD.
The team also found that each 1-minute reduction was linked with worsening strain. However, test duration or change in fitness was not associated with CAC.
Commenting on this finding, the researchers write:
"The finding that fitness is related to development of subclinical changes in myocardial structure and function, but not CAC, sheds light on potential mechanistic benefits of exercise in youth not captured by CAC."
They add that they "were surprised to find that fitness (or its change over time) was not associated with the extent or the presence of CAC in long-term follow-up."
Reducing obesity 'not the only benefit of early adulthood fitness'
As a result of their findings, the researchers say that efforts to improve early adulthood fitness "may affect long-term health at the earliest stages in CVD pathogenesis."
In a linked commentary, Drs. David E. Chiriboga and Ira S. Ockene, of the University of Massachusetts Medical School in Worcester, write:
"The present report draws attention to the substantive and independent value of physical activity and CRF in CVD prevention regardless of age, race or sex, highlighting its significance as a tool for individuals and population-based intervention.
Policies directed at promotion of physical activity in the population will have a significant effect on CVD morbidity and mortality."
The study authors note that their findings could not be explained entirely by body mass index (BMI), weight changes or cardiometabolic disease, which suggests that reducing obesity - and its ill effects - "may not be the only mechanism of benefit of being fit early in adulthood."
Medical News Today recently reported on a study that suggested there are some cases where vigorous exercise can actually be bad for the heart.