To the Editor: Dr Lee and colleagues found that at least 1 hour of recreational walking per week was associated with lower rates of coronary heart disease (CHD) in healthy female professionals aged 45 years and older who participated in no other vigorous activity.1 We are concerned that health professionals and the public could easily misinterpret the appealing take-home message of Lee et al that "no pain, no gain is passé" and assume that 1 h/wk of any walking is sufficient for reducing the risk of chronic disease. Because the cardiovascular benefits reported in the study by Lee et al occurred in minimally active women compared with women who do no activity at all, such benefits cannot be generalized to the population as a whole.

We are especially concerned because the majority of US adults report they already walk at least 1 h/wk. During 1999-2000, we used a national random-digit dial survey to ask 7529 adults aged 18 years and older, "In a usual week, do you walk for at least 10 minutes at a time while at work, for recreation, exercise, to get to and from places or for any other reason?" Sixty-nine percent of both male and female respondents reported walking at least 60 min/wk (95% confidence interval, 67.8%-70.4%). Based on the main finding in the study by Lee et al, these respondents might erroneously conclude that there is little additional benefit to be obtained from further increasing their activity level.

The rapidly increasing rates of obesity and type 2 diabetes mellitus are testimony to the inadequacy of physical activity levels among US adults.2-3 As noted by Lee et al, 1 h/wk of walking falls far short of national guidelines, which recommend that adults should accumulate at least 30 minutes of moderate-intensity level of activity (equivalent to brisk walking) on most, and preferably all, days of the week.4 Even this activity level is the minimum recommended, and persons who already meet it "are likely to derive some additional health and fitness benefits from becoming more physically active."4

The message that even small increases in activity can result in demonstrable health benefits certainly should be promoted to the sedentary population, and walking 1 h/wk is a great beginning toward meeting national guidelines. Encouraging the sedentary population to get moving is critical, but in doing so we must not inadvertently discourage the vast majority of adults who are already minimally active from making further progress.

Janet H. Bates, MD,MPH; Mary K. Serdula, MD,MPH; Laura Kettel Khan, PhD; Deborah A. Jones, PhD,RD; Caroline A. Macera, PhD
Division of Nutrition and Physical Activity
National Center for Chronic Disease Prevention and Health Promotion
Centers for Disease Control and Prevention
Atlanta, Ga
Barbara E. Ainsworth, PhD,MPH
Departments of Epidemiology and Biostatistics and Exercise Science
School of Public Health
University of South Carolina
Columbia

1. Lee I-M, Rexrode KM, Cook NR, Manson JE, Buring JE. Physical activity and coronary heart disease in women: is "no pain, no gain" passé? JAMA. 2001;285:1447-1454. ABSTRACT/FULL TEXT
2. Mokdad AH, Serdula MK, Dietz WH, Bowman BA, Marks JS, Koplan JP. The spread of the obesity epidemic in the United States, 1991-1998. JAMA. 1999;282:1519-1522. ABSTRACT/FULL TEXT
3. Mokdad AH, Ford ES, Bowman BA, et al. Diabetes trends in the U.S.: 1990-1998. Diabetes Care. 2000;23:1278-1283. ABSTRACT
4. Pate RR, Pratt M, Blair SN, et al. Physical activity and public health: a recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA. 1995;273:402-407.

To the Editor: Dr Lee and colleagues1 suggested that even low-level exercise appears protective against CHD. Unfortunately, association studies cannot clarify whether the exercise causes these improved outcomes. As the authors point out, although the intensity of activity was much less than the reported activity in most earlier studies, the group differences observed were substantial and significant. The results of Lee et al also show no trend to improved outcomes for progressively more vigorous activity; although there was a significant but small trend toward benefit from increased energy expenditure, the group that expended 600 to 1499 kcal/wk actually had better outcomes than the group that expended 1500 kcal/wk and greater (Table 2). People older than 65 years who participated in social and productive activities, usually involving minimal physical activity, have been found to have significantly lower mortality over 13 years than nonparticipators,2 and the magnitude of mortality reduction was quite similar to the reductions of CHD noted by Lee et al. This near absence of dose-benefit relationship weakens the cause-effect hypothesis.