Calcium and iron
Supplements are meant to restore missing vitamins and nutrients but this is not possible if they are paired wrong and cancel each other out.
According to Trista Best, MPH, RD, a registered dietitian at Balance One Supplements, calcium and iron are among the worst combinations out there, undermining one another’s effects. “These two vitamins compete for absorption, and calcium will reduce the amount of iron your body is able to absorb, if any.”
The best combination for an efficient absorption of iron is iron and vitamin C supplements, says Best. Vitamin C helps iron absorption from non-heme irons aka plant sources. Just add some lemon to your water or consume fruits that are rich in vitamin C such as strawberries.