Digit ratio – a putative measure of prenatal sex steroids – may be related to body mass index (BMI). However, reports of correlations between 2D:4D and BMI have yielded mixed results with some studies showing no relationship while others have reported positive associations in men or women only. This study considers associations between self-reported 2D:4D and BMI in a large online survey (i.e. the BBC Internet Study). At the individual level, there was a weak positive association between 2D:4D and BMI in both sexes with greater effect sizes in women. Body mass index was positively related to age and negatively related to parental income; however, the relationship between 2D:4D and BMI was independent of both variables. At the national level, mean 2D:4D per country showed positive associations with mean national BMI but those correlations were restricted to females. It is concluded that BMI is positively related to low prenatal testosterone and high prenatal oestrogen. Parental income inequality may influence both prenatal sex steroids (through a ‘Trivers–Willard’ effect) and BMI such that increases in inequality result in reductions in prenatal testosterone and increases in BMI at the individual and national level.

数字比率 - 产前性类固醇的推定测量 - 可能与体重指数（BMI）有关。然而，关于 2D:4D 和 BMI 之间相关性的报告产生了不同的结果，一些研究显示没有关系，而另一些研究报告仅在男性或女性中呈正相关。这项研究在一项大型在线调查（即 BBC 互联网研究）中考虑了自我报告的 2D:4D 和 BMI 之间的关联。在个体层面，2D:4D 与 BMI 之间存在弱正相关，在女性中影响更大。体重指数与年龄呈正相关，与父母收入呈负相关；然而，2D:4D 和 BMI 之间的关系与这两个变量无关。在国家层面，平均 2D：每个国家的 4D 与平均国家 BMI 呈正相关，但这些相关性仅限于女性。得出结论，BMI与产前低睾酮和高产前雌激素呈正相关。父母收入不平等可能会影响产前性类固醇（通过“特里弗斯-威拉德”效应）和 BMI，因此不平等的增加会导致产前睾酮的减少和个人和国家层面的 BMI 增加。