Table 2.
Overall and stratified meta-analyses of relative risk estimates (associations) for physical activity and risk of colorectal cancer by BMI subgroups
| Overall/stratified analysis | Total number of estimates | Number of casesa | Pooled RR (95% CI) | I2 (%) | Pheterogeneity | P across subgroups | P across high and low BMI |
|---|---|---|---|---|---|---|---|
| Low BMI | |||||||
| Overall | 27 | 7045 | 0.74(0.66–0.83) | 47.9 | 0.003 | ||
| Sex | |||||||
| Male | 12 | 2590 | 0.76 (0.64–0.92) | 53.1 | 0.015 | 0.551 | |
| Female | 8 | 1639 | 0.72 (0.57–0.91) | 33.6 | 0.160 | ||
| Both | 7 | 2816 | 0.70 (0.56–0.89) | 50.2 | 0.061 | ||
| Study Design | |||||||
| Cohort | 11 | 3073 | 0.76 (0.61–0.94) | 59.3 | 0.006 | 0.088 | |
| Case-control | 16 | 3972 | 0.72 (0.62–0.84) | 40.7 | 0.046 | ||
| Cancer Site | |||||||
| Colon | 17 | 3436 | 0.69 (0.59–0.81) | 41.5 | 0.038 | 0.410 | |
| Colorectal | 6 | 2854 | 0.74 (0.56–0.98) | 55.6 | 0.047 | ||
| Rectal | 4 | 755 | 0.94 (0.83–1.06) | 0.0 | 0.942 | ||
| Interactionb | |||||||
| No | 13 | 3128 | 0.78 (0.66–0.92) | 37.3 | 0.004 | 0.462 | |
| Yes | 14 | 3917 | 0.70 (0.59–0.84) | 57.6 | 0.085 | ||
| Physical Activity Type | |||||||
| Total | 9 | 2681 | 0.74 (0.61–0.89) | 32.7 | 0.156 | 0.605 | |
| Recreational | 12 | 3874 | 0.78 (0.64–0.94) | 60.5 | 0.003 | ||
| Commuting | 6 | 490 | 0.64 (0.51–0.79) | 0.0 | 0.675 | ||
| Physical Activity Measurement | |||||||
| Adulthood/lifetimec | 16 | 5151 | 0.72 (0.64–0.82) | 16.0 | 0.271 | 0.497 | |
| Past year or two | 6 | 1319 | 0.75 (0.56–1.01) | 67.8 | 0.008 | ||
| Regulard | 5 | 575 | 0.77 (0.51–1.17) | 63.8 | 0.026 | ||
| Physical Activity Assessment | |||||||
| MET-h/day or week | 13 | 2188 | 0.73 (0.62–0.87) | 52.4 | 0.014 | 0.969 | |
| Kcal/week | 2 | 1993 | 0.75 (0.54–1.04) | 0.0 | 0.437 | ||
| Times/week or month | 3 | 1939 | 0.75 (0.53–1.05) | 78.1 | 0.010 | ||
| Othere | 9 | 925 | 0.72 (0.54–0.98) | 41.6 | 0.090 | ||
| Physical Activity Reference Group | |||||||
| No activity | 9 | 4453 | 0.70 (0.57–0.85) | 41.9 | 0.088 | 0.538 | |
| Some activity | 18 | 2592 | 0.76 (0.65–0.88) | 47.8 | 0.013 | ||
| Geographical Region | |||||||
| North America | 12 | 5026 | 0.82 (0.71–0.94) | 47.7 | 0.033 | 0.122 | |
| Europe | 5 | 920 | 0.60 (0.38–0.93) | 59.2 | 0.044 | ||
| Asia | 8 | 824 | 0.66 (0.55–0.80) | 7.4 | 0.373 | ||
| Australia | 2 | 275 | 0.71 (0.38–1.30) | 0.0 | 0.482 | ||
| High BMI | |||||||
| Overall | 36 | 9407 | 0.65 (0.53–0.79) | 89.0 | <0.001 | 0.389 | |
| Sex | |||||||
| Male | 17 | 2928 | 0.56 (0.34–0.94) | 74.9 | <0.001 | 0.268 | 0.264 |
| Female | 9 | 1568 | 0.61 (0.47–0.79) | 92.1 | <0.001 | 0.333 | |
| Both | 10 | 4911 | 0.83 (0.65–1.05) | 82.8 | <0.001 | 0.384 | |
| Study Design | |||||||
| Cohort | 15 | 4625 | 0.93 (0.78–1.13) | 64.1 | <0.001 | 0.002 | 0.178 |
| Case-control | 21 | 4782 | 0.51 (0.39–0.66) | 88.0 | <0.001 | 0.053 | |
| Cancer Site | |||||||
| Colon | 20 | 5330 | 0.58 (0.44–0.79) | 91.5 | <0.001 | 0.282 | 0.435 |
| Colorectal | 9 | 2841 | 0.74 (0.49–1.11) | 85.9 | <0.001 | 0.948 | |
| Rectal | 7 | 1236 | 0.74 (0.62–0.88) | 4.1 | 0.395 | 0.052 | |
| Interactionb | |||||||
| No | 18 | 4881 | 0.87 (0.79–0.96) | 0.0 | 0.761 | 0.001 | 0.220 |
| Yes | 18 | 4526 | 0.48 (0.34–0.68) | 93.4 | <0.001 | 0.081 | |
| Physical Activity Type | |||||||
| Total | 13 | 4141 | 0.81 (0.68–0.96) | 40.4 | 0.065 | <0.001 | 0.424 |
| Recreational | 19 | 4830 | 0.74 (0.61–0.91) | 75.3 | <0.001 | 0.810 | |
| Commuting | 4 | 436 | 0.21 (0.14–0.32) | 81.9 | 0.001 | 0.001 | |
| Physical Activity Measurement | |||||||
| Adulthood/lifetimec | 20 | 7082 | 0.54 (0.40–0.73) | 93.5 | <0.001 | 0.022 | 0.179 |
| Past year or two | 10 | 1985 | 0.75 (0.64–0.87) | 3.5 | 0.408 | 0.780 | |
| Regulard | 6 | 340 | 1.00 (0.73–1.38) | 21.7 | 0.270 | 0.366 | |
| Physical Activity Assessment | |||||||
| MET-h/day or week | 13 | 2411 | 0.55 (0.37–0.81) | 90.8 | <0.001 | 0.086 | 0.224 |
| Kcal/week | 5 | 2058 | 0.57 (0.45–0.72) | 20.3 | 0.285 | 0.251 | |
| Times/week or month | 5 | 3549 | 0.90 (0.67–1.19) | 87.9 | <0.001 | 0.478 | |
| Othere | 13 | 1389 | 0.77 (0.59–1.00) | 49.8 | 0.030 | 0.778 | |
| Physical Activity Reference Group | |||||||
| No activity | 14 | 8521 | 0.77 (0.67–0.87) | 41.2 | <0.001 | 0.132 | 0.474 |
| Some activity | 22 | 4745 | 0.57 (0.40–0.82) | 92.4 | 0.054 | 0.199 | |
| Geographical Region | |||||||
| North America | 21 | 6990 | 0.75 (0.64–0.87) | 69.6 | <0.001 | 0.127 | 0.525 |
| Europe | 7 | 1239 | 0.67 (0.45–0.99) | 69.9 | 0.003 | 0.724 | |
| Asia | 6 | 583 | 0.36 (0.19–0.66) | 92.0 | <0.001 | 0.090 | |
| Australia | 2 | 595 | 0.98 (0.57–1.68) | 45.1 | 0.177 | 0.520 | |
Abbreviations: BMI body mass index, MET metabolic equivalent of task
aBMI subgroup-specific case numbers were not described for Gerhardsson (1990) [30] Slattery (1997) [36], thus total cases were used for case numbers from these two studies
bEstimates representing an interaction between physical activity and BMI on colorectal cancer risk
cStudies with over 10 years of physical activity measurement were included in this category
dTime period of measurement not specified
eOther measures include a study’s own physical activity index or unique classification of active vs. inactive individuals