Nearly all of us are deficient in vitamin D. Ninety percent of our body's vitamin D comes from the sun, meaning cholesterol in our skin is converted into vitamin D3 (cholecalciferol) by the action of UV rays from the sun. Vitamin D3 is then converted by the liver and kidneys into the active form of vitamin D. The other 10% of out body's vitamin D3 comes from our diet. If you live in Canada you are probably vitamin D deficient. The rates are so high the BC government health plan no longer pays for testing - they want us to just assume we are deficient. That's fair as we know there are health benefit to taking vitamin D whether you are really deficient or just a little. In any case, we should all be taking vitamin D (with a few rare exceptions).
A meta-analysis was just published this month on vitamin D and fertility. The meta-analysis reviewed all studies (11 total) that examined vitamin D levels in women and IVF outcomes. Bottom line: you are 33% more likely to have a baby from IVF if you had good vitamin D levels. There was no impact on miscarriage rates, so it seems the impact of vitamin D is at the level of embryo implantation. It seems embryos are more likely to stick to the uterus and flourish if vitamin D levels are normal.
Until now the benefit of vitamin D has been thought to be to eggs. Because vitamin D levels influence how calcium moves and is used in cells, it has been thought that low vitamin D was damaging to egg health. There is evidence from animal studies that vitamin D might effect chromosome health too. For this reason I have been suggesting infertile women take vitamin D. More recently we have come to realize vitamin D helps with embryo implantation in the uterus.
It matters whether the benefit of vitamin Ds at the egg and/or at implantation. It matters as we treat hundreds of women with donor eggs every year. If the benefit is only on egg quality, then they don't need to take extra vitamin D, but if the benefit is at the time of implantation, then the should. While there is a little controversy as to how much women using donor eggs benefit from vitamin D supplementation, I am convinced enough to recommend it to my donor egg patients too.
So, in my opinion, all women undergoing IVF (with their own eggs or donor eggs) should be taking vitamin D. The dose? It has varied study to study but I recommend 2000 IU. While I a not trying to get pregnant now (or ever again - my family is complete) I personally, I take vitamin D 1000 IU drops 0-6 times per week. I am terrible at remembering to take them so when I do remember I typically take 3000-4000 IU at once. Vitamin D is fat soluble so it can accumulate in your body and there is no evidence of toxicity in taking it in periodic, high doses like this. So, for the forgetful - take it when you remember and try to get about 2000 IU per day, on average.
Next question: what is the role of vitamin D in sperm health?