Vitamin d3 with tamoxifen

Hi, I wasn't told to, but am taking it along with other vitamins. I was told just to make sure I was only taking the recommended dose of any vitamins (alongside Tamoxifen) and to still ask the oncologist or breast care nurses before taking any herbal supplements (the same as when having chemo).

I'm on letrozole not Tamoxifen, but my oncologist started me on vitamin D with chemo (several huge doses then 1000 iu daily for life. She checked I was still taking it 3 months after chemo at my appointment too. It apparently lowers the rist of cancer (amongst other illness), and can lower ostrogen levels too https://www.avogel.co.uk/food/how-does-vitamin-d-affect-your-hormones/