Age at voice break in Danish boys: effects of pre-pubertal body mass index and secular trend.

Voice break is a late, but characteristic event in male puberty. Assessment of age at voice break may be a relevant marker for epidemiological studies of male pubertal development. We investigated the timing of voice break and its association with explanatory variables [calendar year of admission in the boys choir and pre-pubertal body mass index (BMI)] by survival analysis techniques based on retrospective analyses of age at voice break in 463 Danish choir boys who were studied over a 10-year period. We found an overall median age at voice break of 14.0 [13.9-14.6] years, and a statistically significant downwards trend in age at voice break in the 10-year period (1994-2003) (log-rank test p = 0.0146). There was a statistically significant difference in age at voice break between boys in the different BMI quartiles in pre-puberty (p = 0.00822) with a tendency towards early voice break with increasing BMI standard deviation scores. Thus boys in the heaviest quartile at 8 years of age had an increased risk of early voice break (RR of 1.74 [1.14-2.65]) approximately 6 years later, compared with boys in the thinnest quartile. The earlier voice break seen during the 10-year observation period could however not exclusively be explained by a general increase in BMI in that period. Our findings indicate that puberty, as assessed by age at voice break in boys, may be starting earlier in Denmark as it has been observed in the USA, and suggest a relationship between pre-pubertal BMI and the timing of puberty.