Women on birth control pills risk becoming vitamin D deficient if they stop taking it, researchers have warned. American scientists have found a link between the hormone estrogen – which is in the pills and some other birth control methods – and raised vitamin D levels. They believe taking the contraceptive could increase levels of the vitamin in the body by around 20 per cent – but stopping the hormonal birth control can cause levels to drop.(1)
On the other hand, birth control pills may be linked to a higher risk of breast cancer. The results of a study looking into risk factors for breast cancer found that using high-dose estrogen birth control pills in the previous year was linked to a 50% increase in the risk of breast cancer compared to women who had never or had formerly used birth control pills.(2) (However, it is worth noting that this study didn’t take into account whether the women had any family history of breast cancer or had an abnormal BRCA1 or BRCA2 gene. Also, results may vary depending of the exact composition of the pills).
(2) “Recent Oral Contraceptive Use by Formulation and Breast Cancer Risk among Women 20 to 49 Years of Age.” Cancer Research, Aug. 1, 2014