Can Vitamin D Boost Fertility?
A Danish natural experiment found the 12-month conception rate among women with infertility was about 15% during years when margarine was fortified with Vitamin D, versus about 9% during years it wasn't -- suggestive, though not proof the effect was Vitamin D alone.
A study looked at whether Vitamin D could actually help increase the odds of getting pregnant -- and the natural experiment behind it is a genuinely clever one.
Vitamin D and... margarine?
Danish researchers looked at a large group of women struggling to conceive. Between 1962 and 1985, Denmark required all margarine to be fortified with Vitamin D (1.25mg per 100g), which raised average Vitamin D intake by about 13%. That mandate ended in 1985. Margarine consumption itself stayed stable through the surrounding years, which let researchers compare conception rates before and after fortification stopped, without a big confound from changing margarine habits.
During the fortified years, the 12-month conception rate among women diagnosed with infertility hovered around 15%. After fortification ended, it dropped to around 9%. Researchers tried to account for other contributing factors, but a natural experiment like this can't fully rule out everything else that changed over time -- so it's suggestive rather than conclusive.
The takeaway
Getting enough Vitamin D is probably a good idea regardless, and it can be genuinely hard to get enough during winter months -- so make an effort to get outside when you can, and consider whether a supplement makes sense for you.
Reference
Jensen et al. (2020). Fertility & Sterility, 113(2), 383–391.
Common questions
Does this study prove Vitamin D improves fertility?
Not definitively -- researchers tried to account for other factors, but it's a natural experiment (comparing time periods), not a randomized trial, so other things could have contributed to the difference.
How can I make sure I'm getting enough Vitamin D?
Sun exposure is a major natural source, and it can be harder to get enough during winter months, so it's worth paying extra attention then.