Alvin B. Lin, MD, FAAFP
Dr. Lin is an associate professor of family and community medicine at University of Nevada School of Medicine and an adjunct professor of family medicine and geriatrics at Touro University Nevada College of Medicine. He also serves as an advisory medical director for Infinity Hospice Care and as medical director of Lions HealthFirst Foundation. Dr. Lin maintains a small private practice in Las Vegas, NV. The posts represent the views of Dr. Lin, and in no way are to be construed as representative of the above listed organizations. Dr. Lin blogs about current medical literature and news at http://alvinblin.blogspot.com/.
Chicken or egg. Which came first? Likewise, exercise vs depression. Which comes first? Does lack of, or insufficient, exercise lead to depression? Or does depression lead to less exercise as a result of anhedonia, less energy, and greater fatigue?
In a prospective epidemiologic study published last month in the American Journal of Preventive Medicine, the authors concluded that cardiorespiratory fitness, as a measure of persistent regular exercise, actually protects against depression as we age. In an attempt to solve this conundrum, the authors followed a community dwelling cohort of men & women interested in their own health and who had volunteered to be studied at the Cooper Clinic's Aerobics Center Longitudinal Study.
The 10,290 participants ranged from ages 20 to 85 (average 49yo at baseline) and were free of depression at the start of the study, which lasted close to 4yrs on average. Cardiorespiratory fitness was measured serially by treadmill, specifically symptom limited time using a modified Balke protocol.
Interestingly, these participants were not necessarily representative of the US population in that the average body mass index for the women was just over 22kg/m2, or well into the normal range (less than 25kg/m2), rather than the overweight (BMI 25-30kg/m2) or obese (greater than 30kg/m2) category in which two thirds of Americans find themselves these days. As expected though, the men were actually overweight w/average BMI 25+.
So just how much exercise does one have to do? Current recommendations are to achieve 30 minutes per day, most days of the week, of moderate intensity exercise. This study suggests that we should use a different metric (cardiorespiratory fitness) to more objectively measure exercise intensity. In fact, the authors noted that a decline in metabolic equivalents achieved on the treadmill was associated with anywhere from 2% - 9.5% greater odds of initial depression. Bottom line, put some effort into your regular exercise; don't dilly-dally around.