Obesity is a pandemic and major risk factor for cancers. The reduction of obesity would have been an effective strategy for cancer prevention, but the reality is that worldwide obesity has kept increasing for decades, remaining a major avoidable cancer risk secondary only to smoke. The present studies suggest that vitamin D may be an effective agent to reduce obesity-associated cancer risks in women. Molecular analyses showed that leptin increased human telomerase reverse transcriptase (hTERT) mRNA expression and cell growth through estrogen receptor alpha (ERα) activation in ovarian cancer (OCa) cells, which was suppressed by 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3]. The suppression was compromised when miR-498 induction by the hormone was depleted with miRNA sponges. In mice, high-fat diet (HFD) stimulation of ovarian tumor growth was remarkably suppressed by 1,25(OH)2D3 analogue EB1089, which was also compromised by miR-498 sponges. EB1089 did not alter HFD-induced increase in serum leptin levels but increased miR-498 and decreased the diet-induced hTERT expression in tumors. Quantitative RT-PCR (qRT-PCR) analyses revealed an inverse correlation between hTERT mRNA and miR-498 in response to 1,25(OH)2D3 in estrogen-sensitive ovarian, endometrial and breast cancers. The studies suggest that miR-498-mediated hTERT down regulation is a key event mediating the anti-leptin activity of 1,25(OH)2D3 in estrogen-sensitive tumors in women.