A higher fitness level in middle age is associated with a lower risk of depression and cardiovascular disease (CVD) mortality some 20 years later, new research shows.
“What’s surprising about this study is the time interval between the measurement of fitness and the outcomes of depression and CVD mortality,” author Benjamin L. Willis, MD, MPH, Director of Epidemiology, Cooper Institute, Dallas, Texas, told Medscape Medical News.
“Something that you’re doing right now can actually provide some benefits many years later, even when you might have a problem, say, of depression that occurs because of some other life event. It’s never too late to get off the couch, but sooner is better,” he added.
The study was published online June 27 in JAMA Psychiatry.
For the study, investigators used the Cooper Center Longitudinal Study (CCLS), a continuation of another ongoing prospective study at the Cooper Institute that began in 1970.
Patients included in the CCLS are generally well-educated non-Hispanic white patients with access to healthcare.
The study included 17,989 patients, of whom 80.2% men, with a mean age of 50.0 years at the midlife examination who had fee-for-service Medicare coverage since January 1, 1999.
Researchers linked information from the CCLS with claims data from the Centers for Medicare & Medicaid Services. They followed participants from the date of initiating Medicare coverage until death or the end of follow-up on December 31, 2009.
Cardiorespiratory fitness levels were measured using a graded treadmill exercise test carried out in clinic under medical supervision. Each participant’s treadmill time was categorized by age- and sex-specific quintiles. Quintile 1 represented low fitness; quintiles 2 and 3, moderate fitness; and quintiles 4 and 5, high fitness.
The outcome of depression was “not clinically adjudicated” but came from Medicare administrative data, said Willis.
Depression was defined using International Classification of Diseases, Ninth Revision (ICD-9) codes.
Mortality information was obtained from the National Death Index. The underlying cause of death was defined by ICD-9 codes for deaths before 1999 and by ICD, 10th Revision (ICD-10) codes for deaths from 1999 through 2009.
Compared with participants in the low fitness category, those in the high fitness category had a lower mean body mass index (BMI), lower systolic blood pressure, and more favorable mean levels of total cholesterol and fasting glucose.
The rate of depression was 22.2 per 1000 person-years in the high fitness category, 26.2 in the moderate fitness category, and 30.7 in the low fitness category
For CVD mortality without incident depression, the rate in the high fitness category was 3.9 deaths per 1000 person-years compared with 5.7 in the moderate fitness category and 10.4 in the low fitness category.
For CVD mortality after depression, the rate in the high fitness category was 16.1 deaths per 1000 person-years versus 25.8 in the moderate fitness category and 32.9 in the low fitness category.
In analyses adjusted for traditional risk factors including age, sex, blood pressure, cholesterol level, BMI, and smoking status, the high fitness category was associated with a 16% lower risk of depression (hazard ratio [HR], 0.84; 95% confidence interval [CI], 0.74 – 0.95) and a 61% lower risk of CVD mortality (HR, 0.39; 95% CI, 0.31 – 0.48) compared with low fitness.
In those with incident depression, high fitness was associated with a 56% lower risk of CVD death (HR, 0.44; 95% CI, 0.31 – 0.64).
As most participants were men, researchers adjusted for gender differences and found that fitness was just as beneficial in women as men, said Willis.
Fitness levels were not re-tested after the midlife examination. “A good research question is the effect of change in fitness over time,” said Willis.
Investigators analyzed the three outcomes — depression and CVD mortality with and without preceding depression — separately.
However, it was not possible to determine whether a higher fitness level reduced the risk of both depression and CVD mortality or if lowering one affected the other.
Willis noted that the role of physical activity as a treatment for depression was not evaluated because individuals with a history of depression were excluded from the study.
Only about half of American adults meet physical activity guidelines by the US Department of Health & Human Services, said Willis, which recommend 150 minutes per week of moderate to vigorous aerobic activity (for example, walking, jogging, swimming, and cycling) plus resistance training twice a week.
“What we have here is a population that is generally inactive,” said Willis. “It’s important, we think, to consider physical activity and cardiorespiratory fitness as part of an overall preventive strategy.”
He added that “if patients can adopt physical activity as part of their lifestyle and behavior, that would be helpful even into older age.”
Although it’s never too late to get active, those with medical conditions or who have long been sedentary should check with their physicians before embarking on an exercise program, said Willis.
The finding that midlife fitness may protect against later depression is “very interesting,” said Robert Roca, MD, vice president and medical director, Sheppard Pratt Health System, and chair, Council on Geriatric Psychiatry, American Psychiatric Association, who holds psychiatry faculty appointments at both the University of Maryland, College Park, and Johns Hopkins University School of Medicine, Baltimore, Maryland, who commented on the study for Medscape Medical News.
However, Roca noted that the article didn’t address the fact that people who are very fit in midlife also tend to be very fit later in life.
“If that’s the case, we don’t know for sure that what they did at midlife was what mattered; it may be that what they’re doing currently is what matters,” he said. “If you were fit at midlife and then were a sloth after that, would that still be protective? That’s not clear to me.”
Another study limitation, which the authors acknowledged, is that the direction of causality is unknown, said Roca.
“It could be that fitness promotes mood improvement or protects against depression; it could also be that people who tend to be depressed don’t tend to be as active,” he said.
He added that his “hunch” is that causality probably goes in both directions.
Fitness is one of Roca’s “favorite interventions” to recommend to people who are depressed. “It’s often difficult to mobilize people who are depressed to be active, but it can certainly be helpful if they are.”
Willis and Roca have reported no relevant financial relationships.
JAMA Psychiatry. Published online June 27, 2018. Abstract