The 1 297 124 women included in our analysis had a mean age at recruitment of 56·1 years (SD 4·9) and an average year of birth of 1942. The median length of follow-up was 9·4 years per woman (IQR 8·4–10·2 years), for a total of 11·7 million person-years, during which 97 376 incident cancers were notified.
shows characteristics of the study population, including measured height, by six categories of height reported at recruitment. Taller women tended to be of higher socioeconomic status, to drink more alcohol, to be more active, to have a later age at menarche, to have fewer children, and to have their first child later in life than shorter women. Taller women were less likely to be obese or to be current smokers. Based on heights measured in the validation sample, the mean height in the study population was 160·9 cm (SD 6·4).
Baseline characteristics by height and follow-up for incident cancer in the Million Women Study
Total cancer incidence rose with increasing height (). Comparing women in the tallest group with those in the shortest group (a difference of 21 cm: mean measured heights 174 cm and 153 cm), the adjusted RR for total incident cancer was 1·37 (95% CI 1·33–1·42; p<0·0001). The RR for total cancer was 1·16 (1·14–1·17; p<0·0001) per 10 cm increase in height ().
Relative risks (RRs) and 95% floated CIs (FCIs) for total cancer incidence, by category of height reported at recruitment (mean measured height)
Relative risks (RRs) and 95% floated CIs (FCIs) for total incident cancer, by height
shows the RRs per 10 cm increase in height for the 17 separate cancer sites we assessed, for all other cancers and for total cancer. The height-associated RRs are greater than 1·0 for 15 of the 17 specific sites, and are significantly increased for ten specific sites and for the group of other and unspecified cancers: colon (RR per 10 cm increase in height 1·25, 95% CI 1·19–1·30), rectum (1·14, 1·07–1·22), malignant melanoma (1·32, 1·24–1·40), breast (1·17, 1·15–1·19), endometrium (1·19, 1·13–1·24), ovary (1·17, 1·11–1·23), kidney (1·29, 1·19–1·41), central nervous system (1·20, 1·12–1·29), non-Hodgkin lymphoma (1·21, 1·14–1·29), leukaemia (1·26, 1·15–1·38), and other cancers (1·15, 1·11–1·20). For no cancer site was there a significant decrease in risk with increasing height. There is heterogeneity across cancer sites (contrast test χ2 [17 degrees of freedom]=115·2; p<0·0001) mostly because of the greater than average increase in risk with increasing height for colon cancer and for malignant melanoma, and the lower than average risk for lung cancer. Breast cancer accounts for half of incident cancers in our study and the results for breast cancer therefore dominate the overall results. However, the overall RR of incident cancer in relation to height was not materially altered when we excluded breast cancer cases from our analysis (RR per 10 cm increase in height 1·15, 95% CI 1·13–1·16).
Relative risks (RRs) and 99% CIs per 10 cm increase in height for incident cancer at 17 specific sites and for total cancer
We adjusted our results in and in by age, region, socioeconomic status, smoking, alcohol, body-mass index, physical activity, age at menarche, parity, and age at first birth. shows the effect of adjustment by potential confounding variables on the RR for total cancer per 10 cm increase in height in an analysis restricted to the 1 087 489 women with full information on all adjustment variables. Compared with the risk with adjustment for age and region only (RR 1·14, 95% CI 1·13–1·15), additional adjustment by the remaining factors increases the RR slightly to 1·16 (1·15–1·18).
Relative risks (RRs) and 95% CIs per 10 cm increase in height, for total incident cancer: effect of adjustment by various factors
shows the RR for total cancer per 10 cm increase in height, and the mean measured height, in subgroups of women defined by their year of birth, socioeconomic status, smoking status, alcohol consumption, body-mass index, physical activity, age at menarche, parity, age at first birth, menopausal status, and use of oral contraceptives and hormone replacement therapy. As we expected, women born before 1939 were shorter than women born in 1946 or later (mean measured height 159·9 vs 161·5 cm), as were women from the lowest compared to the highest socioeconomic tertile (160·1 vs 161·4 cm). However, the height-associated RR for total cancer did not vary significantly by these or by most other characteristics. shows this lack of variation by socioeconomic status. Although the risk for total cancer is somewhat higher in women in the lowest tertile of socioeconomic status, the pattern of risk by height is similar in all three tertiles. Of the 12 personal characteristics we assessed, only smoking status substantially modified the size of the height-related RRs (). The RR per 10 cm greater height was 1·19 (95% CI 1·17–1·21) in never smokers, but only 1·11 (1·08–1·14) in current smokers (p<0·0001 for heterogeneity).
Relative risks (RRs) and 99% CIs per 10 cm increase in height for all incident cancer, by various characteristics at recruitment
Relative risks (RRs) and 95% floated CIs (FCIs) for all incident cancer in relation to height, and by socioeconomic status
shows the RRs per 10 cm increase in height by cancer site in never smokers and in current smokers (results in past smokers are uninterpretable, because they are a heterogeneous group with a wide range of times since last smoking). The mix of cancers differs in the two groups with, as expected, a higher proportion of women with lung and other smoking-related cancers in current smokers than in never smokers. In never-smokers, heterogeneity across cancer sites was substantially weaker (p=0·004) than in current smokers (p<0·0001).
Relative risks (RRs) and 99% CIs per 10 cm increase in height, for all incident cancer and for incident cancer at 17 specific sites, in never and current smokers
For smoking-related cancers, the RR per 10 cm greater height was substantially smaller in current smokers than in never smokers (1·05 vs 1·17, p for difference=0·0004; ). By contrast, for other specified cancers height-associated RRs were similar in current smokers and in never smokers, and close to our estimate for smoking-related cancers in never smokers ().
Relative risks (RRs) and 95% CIs per 10 cm increase in height for incident smoking-related and other specified cancers, in never and in current smokers
Published evidence suggests that current smoking is not a strong risk factor for colorectal cancer20
and the number of these cancers is large, so we undertook a sensitivity analysis with colorectal cancer classed as not related to smoking (ie, as in the latest full report on smoking and cancer available from IARC11
). The overall pattern of RRs remained similar, with lower risk for smoking-related cancers than for other cancers in current smokers, although the difference between these risks was reduced (RR per 10 cm height 1·02, 95% CI 0·97–1·06, in current smokers and 1·10, 1·03–1·17, in never smokers; p for difference=0·05); for other specified cancers, risks remained similar to those in our main analysis (RRs 1·18, 1·14–1·22, in current smokers and 1·19, 1·16–1·21, in never smokers).
Because breast cancer dominates our findings, we repeated our analyses shown in separately for the five most common cancers in our study: breast, lung, colon, endometrium, and ovary, and for the remaining cancers. Overall, we did not identify significant heterogeneity, by the 12 factors we show in , for these cancer sites (χ2 test for heterogeneity aggregated across all characteristics: colon p=0·7, lung p=0·2, breast p=0·3, endometrium p=0·5, ovary p=0·2, remaining cancers p=0·2).
Because there was no strong variation by cancer site in our study except in smokers, we did a meta-analysis of published studies of all-cancer risk, noting for each study the proportion of current smokers in the study population. shows details of our study together with ten other prospective studies1,3,8,21–28
that have published results in such a way as to allow estimation of the RR of total cancer incidence or mortality per 10 cm increase in height. The populations covered include men and women from Asia, Australasia, Europe, and North America, with mean years of birth ranging over three decades (1917 to 1946), and with mean heights ranging over 24 cm (155 to 179 cm). The overall increase in RR per 10 cm greater height is 1·14 (95% CI 1·13–1·15). There was no significant heterogeneity between the results from studies in men (I2
for heterogeneity 0%, p=0·9) or between those in women (I2
for heterogeneity 31%, p=0·2), but there was a slightly lower height-associated RR in men than in women (1·10 vs
1·15, p for difference <0·0001). When we excluded the findings of our study, the summary RR in women was slightly reduced (summary RR per 10 cm greater height 1·13, 95% CI 1·10–1·16; I2
for heterogeneity 25%; p=0·2), and there was no longer significant heterogeneity between studies in men and those in women (p for difference=0·1). In our meta-analysis we included studies of cancer mortality as well as those of cancer incidence. All of the mortality studies we included provided RRs adjusted for at least one measure of socioeconomic status, which should have minimised potential confounding due to the relation in many populations between socioeconomic status and cancer survival.29
Meta-analysis of results from prospective studies: study-specific and summary relative risks (RRs) and 95% CIs for all cancer per 10 cm increase in height