To the Editor:
Numerous studies have demonstrated a strong inverse relationship between physical fitness during middle and older ages and subsequent mortality.1–5 Likewise, a lack of physical fitness during adolescence is associated with the subsequent development of cardiovascular risk factors such as obesity.6 However, it has not been reported whether physical fitness during adolescence could be a predictor of long-term mortality. We investigated this in a historical cohort of Japanese women.
All 510 female students (mean age = 16.8 [SD, 2.0] years) from Ochanomizu University Senior High School underwent a physical fitness examination in December 1943. The observational period ended in April 2007. The subjects’ vital status was determined through records of the alumni association, and the follow-up rate was 98%. Subjects who died before the age of 20 years were excluded.
The physical fitness of each subject was determined by the sum of scores for 4 fitness performance tests (a 1000-m run, rope skipping [time until failure to skip;frequency of rope turn, 100-120/min], throwing a 300-g wooden club [distance], and running while carrying a heavy weight [total time to run 100 m with a 16-kg weight]). Each of these 4 tests was assigned a score of 1–10 based on a decile, with 1 representing the lowest level of performance. Thus, the physical fitness score could range from 4 to 40. All analyses were performed using SPSS 15.0 for Windows (Chicago, IL).
During 64 years of observation (30,823 person-years), 72 women died. Using Kaplan-Meier analysis with log-rank tests, cumulative all-cause mortality in subjects with a total score above 22 (the median) was lower than in those with a score below the median (P = 0.027; Figure).
Our results demonstrated that a high degree of physical fitness early in life was associated with lower mortality.1-5 The difference between curves of those with low and high physical fitness was remarkable before 50 years of age and after 70 years of age. The difference in premature death could have been partially modified by malnutrition or infection such as tuberculosis, which was a leading cause of death during the postwar period. The reasons for the difference in later deaths are yet to be determined. However, cardiovascular disease, which accounts for one-third of mortality in the general population of Japanese women, may be a candidate, based on findings of a recent review,6 suggesting that both cardiorespiratory and muscular fitness are associated with cardiovascular disease risk factors.
This study has several limitations. First, these data are only on Japanese women. Second, causes of death are unknown. Third, information on lifestyle factors at baseline and during the observational period is not available, and so we cannot adjust the results by these parameters. Despite these limitations, our results suggest that a low level of physical fitness even during adolescence could be a risk factor for mature and premature death in Japanese women.
Department of Lifestyle Medicine Ochanomizu University Tokyo, Japan, email@example.com
The authors thank Emiko Suzuki at the Ochanomizu University, Kazuko Sakurai, Toshiko Kobayashi, Yoko Nakatani, Syoko Oshita, staff and member (all from the alumni association of Ochanomizu University Senior High School), Kazuhiko Murooka, Hajime Nagano, Tomoko Ishii, and Kayano Masuda (all from Ochanomizu University Senior High School) for providing assistance in the acquisition of the data.
Supported in part by the Japanese Ministry of Health, Labor and Welfare, as well as the Japan Society for the Promotion of Science.
1. Wei M, Kampert JB, Barlow CE, et al. Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men. JAMA.
2. Sawada S, Muto T. Prospective study on the relationship between physical fitness and all-cause mortality in Japanese men. Nippon Koshu Eisei Zasshi.
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3. Kokkinos P, Myers J, Kokkinos JP, et al. Exercise capacity and mortality in black and white men. Circulation.
4. Mora S, Redberg RF, Cui Y, et al. Ability of exercise testing to predict cardiovascular and all-cause death in asymptomatic women: a 20-year follow-up of the lipid research clinics prevalence study. JAMA.
5. Gulati M, Pandey DK, Arnsdorf MF, et al. Exercise capacity and the risk of death in women: the St James Women Take Heart Project. Circulation.
6. Ortega FB, Ruiz JR, Castillo MJ, Sjostrom M. Physical fitness in childhood and adolescence: a powerful marker of health. Int J Obes (Lond