medwireNews: Data from Taiwan suggest that a younger age at first birth may be protective against kidney cancer in women.
The study - which is the first to assess the role of parity in kidney cancer risk in an Asian population -found no association between the number of births and mortality incidence, however.
Analyzing all 1,292,462 first births in the country between 1978 and 1987, the authors, Chun-Yuh Yang (Kaohsiung Medical University, Taiwan) and colleagues, found that 95 mothers died from kidney cancer by the end of 2009 (0.27 cases per 100,000 person-years).
The kidney cancer mortality rate was 0.36 per 100,000 person-years in women who had given birth to one child, 0.29 in those who had given birth to two, and 0.23 in those who had three or more children, but these differences were not statistically significant.
However, after adjusting for a range of confounders including parity, the authors found that increasing age at first birth was significantly associated with increased risk for kidney cancer death.
For example, those who gave birth after the age of 26 years had a 2.5-fold increased risk for kidney cancer death compared with those who gave birth before the age of 24 years (0.43 vs 0.16 per 100,000 person-years). And, women who gave birth aged 24 to 26 years had a 1.9-fold increased risk (0.31 per 100,000 person-years).
The rate of kidney cancer in women is around half that observed in men. Additionally, obesity, in which fat may provide a major source of endogenous estrogen exposure, is a consistent risk factor for the disease. This has led to the hypothesis that hormonal and reproductive factors may play an important role in the development of the disease, explain the authors in the European Journal of Public Health.
However, theirs is the first study to show that age at first birth is associated with risk for kidney cancer. They say it may be that early exposure to some hormones, including estrogen and progesterone, has a protective effect. However, currently there is not enough evidence to support this.
"Clearly, more work will be needed before the influence of age at first birth on the risk of kidney cancer is understood," the authors conclude.
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