Favors the reduction of estrogens and androgens. Also has 20-alpha-HSD activity. Uses preferentially NADH. 17beta-estradiol + NAD(+) = estrone + H(+) + NADH 17beta-estradiol + NADP(+) = estrone + H(+) + NADPH Steroid biosynthesis; estrogen biosynthesis. Homodimer. Belongs to the short-chain dehydrogenases/reductases (SDR) family.