Letters to the Editor
To the Editor:
Baste et al1 recently presented findings regarding reproductive health among Norwegian female hairdressers. Retrospective data were collected from 12,054 women, whereof 83 were working as hairdressers at the time of the study, and a further 138 women had previously done so. As controls, 10,291 women with other occupations were used. Smoking was assessed as ever having smoked versus never having smoked. In stratified analyses, the highest risks were found for hairdressers who had never smoked, whereas hairdressers who were smokers or ex-smokers had increased risk for infertility but not for delayed conception (≥12 months until conception) or spontaneous abortion.
We have previously presented results for reproductive outcomes among 2626 Swedish female hairdresser compared with 2860 women from the general Swedish population.2 The fractions of women who smoked before (30% vs 27%) or during (18% vs 19%) pregnancy were similar among the hairdressers and the controls. Including smoking habits in the statistical models changed the effect estimates only marginally, that is why the adjusted results were not presented. During the analyses, we did investigate a possible interaction between smoking habits and working as a hairdresser. Because, we did not find any such interaction, we refrained from presenting the results. Nevertheless, in the light of the recent publication by Baste et al,1 we feel compelled to report our findings.
In our original article,2 we presented results for time to pregnancy as a continuous variable. However, to enable comparisons with the results given by Baste et al,1 we have dichotomised time to pregnancy at 12 months. Thus, we have created the outcome “delayed conception.” For both this and spontaneous abortion, we have used logistic regression to estimate the odds ratio with 95% confidence interval.
As can be seen in Table 1, our data do not support that non-smoking hairdressers are at higher risk than the three other groups. It is, however, noteworthy that our data do not suggest any risk for delayed conception or spontaneous abortion associated with smoking in the control cohort. The response rate in our study was rather low (50% among hairdressers and 54% among controls), and we cannot rule out that bias with respect to smoking habits may exist. As pointed out by Baste et al,1 the majority of the results presented on reproductive health among female hairdressers have not considered smoking as neither confounder nor effect modifier. Therefore, the question regarding a possible interaction between smoking habits and working as a hairdresser should remain open.
Anna Axmon, PhD
Lars Rylander, PhD
Division of Occupational and Environmental Medicine Lund University Lund, Sweden
1. Baste V, Moen BE, Riise T, Hollund BE, Oyen N. Infertility and spontaneous abortion among female hairdressers: The Hordaland Health Study. J Occup Environ Med
2. Axmon A, Rylander L, Lillienberg L, Albin M, Hagmar L. Fertility among female hairdressers. Scand J Work Environ Health