Left-handed women are more than twice as likely as right-handers to suffer from breast cancer before reaching menopause, Dutch scientists said on Monday.

More than a million women are diagnosed with breast cancer worldwide each year.

Three-quarters of cases occur after menopause, which usually begins around the age of 50.

Researchers at the University Medical Center in Utrecht in the Netherlands speculate that there is a shared origin early in life for both left handedness and developing breast cancer, possibly exposure to hormones¹ in the womb.

"Left handedness is associated with breast cancer, most specifically pre-menopausal breast cancer," said Cuno Uiterwaal, an assistant professor of clinical epidemiology at the university, in an interview.

He and his colleagues studied 12,000 healthy, middle-aged² women born between 1932-1941 who were part of a breast screening program. The scientists determined³ their hand preference and followed up their medical history to see which women developed breast cancer.

"If we take pre-menopausal and post-menopausal breast cancer then there was a 40 percent increased risk," Uiterwaal said of left-handed women.

But when they spilled it further the scientists found most of the excess risk was in breast cancer before the menopause.

"We found that left-handed women are more than twice as likely to develop pre-menopausal breast cancer as non-left handed women," the researchers said in the report published online by the British Medical Journal.

Other risk factors such as family history of breast cancer, numbers of pregnancies⁴, smoking habits, and social and economic status were considered.

About 8 percent to 9 percent of women are left-handed. But the scientists said the findings should not alarm them.

"What our study intends to do is focus on this area. We do not know all the causes of breast cancer, that is why we should continue. This may be one new factor that leads us to a better understanding of the aetiology (cause of the illness)," Uiterwaal added.

About 5 percent to 10 percent of breast cancers are hereditary⁵. Most are due to mutations in the BRCA1 or BRCA2 genes⁶. The earlier the illness is diagnosed and treated, the better the prognosis is for the woman.

"Although the underlying⁷ mechanisms⁸ remain elusive⁹, our results support the hypothesis that left handedness is related to increased risk of breast cancer," the researchers added. 

　　荷兰研究人员日前表示，那些“左撇子”女性在绝经前更容易患乳腺癌，她们患乳腺癌的危险是习惯用右手的女性的两倍还多。

　　据路透社9月25日报道，每年在全世界范围内有超过100万的女性被诊断出患有乳腺癌，其中有四分之三的病例都是在绝经后发生的。荷兰乌得勒支大学医疗中心的研究人员推测说，左撇子女性和乳腺癌患者在生命早期阶段会经历一个共同的因素，即在母体子宫时可能接触了一些激素。

　　该大学的临床流行病学助理教授屈诺·厄依泰尔瓦尔和他的同事对出生在1932年至1941年间的1.2万名身体健康的中年妇女进行了跟踪研究。这些妇女是接受一项乳腺检查计划的组成人员。研究人员对这些妇女是否是左撇子进行了确定，同时对她们的医疗记录了进行跟踪分析，看后来都有哪些女性患上了乳腺癌。

　　研究结果显示，如果把绝经前乳腺癌患者和绝经后乳腺癌患者都算上的话，左撇子妇女患此病的危险要比不是左撇子妇女多大约40％。而当研究人员把绝经前后患乳腺癌的妇女分开研究时，发现在绝经前左撇子妇女更容易患乳腺癌。

　　对此，厄依泰尔瓦尔表示：“我们发现，在绝经前，左撇子妇女患乳腺癌的危险是习惯使用右手的妇女的两倍还多。”而其它一些患病因素，如乳腺癌的家庭史、怀孕次数、是否吸烟以及社会及经济地位等都已在考虑范围之内。

　　报道说，在所有女性中，大约只有8％至9％的人为左撇子。有5％至10％的乳腺癌患者是由于家族遗传因素造成的；其它大部分人是由BRCA1或BRCA2基因突变引起的。