Favors the reduction of estrogens and androgens. Converts estrone (E1) to a more potent estrogen, 17beta-estradiol (E2) (PubMed:8994190). Also has 20-alpha-HSD activity. Uses preferentially NADH. 17beta-estradiol + NAD(+) = estrone + H(+) + NADH 17beta-estradiol + NADP(+) = estrone + H(+) + NADPH NADP(+) + testosterone = androst-4-ene-3,17-dione + H(+) + NADPH Steroid biosynthesis; estrogen biosynthesis. Homodimer. Exists predominantly as an homodimer but also exits as monomer. Belongs to the short-chain dehydrogenases/reductases (SDR) family.