Supplement pairs
Can I take these together?
Which supplements can be taken together, which are better at different times of day, and where no source gives a rule — answered from NIH, NHS and other official sources. Every fact links to its source.
Taken together
The sources describe them together, and none says to separate them.
- Magnesium and vitamin DYes, togetherYes. No source we checked says to separate them. The NIH notes that magnesium affects levels of the active form of vitamin D, and a review reports that the enzymes that process vitamin D in the liver and kidneys seem to need magnesium as a cofactor. No official source gives a set time of day for the pair.
- Iron and vitamin CYes, togetherYes. NIH says vitamin C (ascorbic acid) enhances the absorption of nonheme iron, the form in plant foods such as beans and vegetables. NHS advice for ferrous sulfate says a doctor or pharmacist may recommend taking it with orange juice or a vitamin C supplement. People with hereditary hemochromatosis should ask a doctor first.
- Vitamin D and calciumYes, togetherYes, they are often combined. NIH says vitamin D is required for the gut to absorb calcium by active transport, and many supplements contain calcium plus vitamin D. No official source says to take them apart. NIH also notes that taking calcium supplements in combination with vitamin D supplements may increase the risk of certain adverse effects.
- Vitamin D and vitamin K2Yes, togetherYes. The NIH says vitamin K supplements are frequently combined with vitamin D, calcium or magnesium, and several vitamin K studies gave vitamin D at the same time. No source we checked says to separate them. Anyone on warfarin should talk to their doctor first, because vitamin K intake needs to stay consistent.
At different times of day
The sources say one can lower how well the other is absorbed.
- Iron and calciumYes, at different timesNot at the same time, according to NIH. Calcium might interfere with iron absorption, although this effect has not been definitively established, so experts suggest taking individual calcium and iron supplements at different times of the day. NHS advice for ferrous sulfate tablets also says calcium can reduce their effect.
- Iron and zincYes, at different timesNot at the same time if the iron dose is high. NIH says taking supplements with 25 mg of elemental iron or more at the same time as zinc supplements can reduce zinc absorption and blood zinc levels. NHS advice for ferrous sulfate tablets says they can stop zinc working as well as it should.
No spacing rule found
No official source describes an interaction or a rule for these two.
- Magnesium and zincNo spacing rule foundNo official source gives a spacing rule for magnesium and zinc. The NIH notes one study in which very high doses of zinc from supplements, 142 mg a day, interfered with magnesium absorption and balance. That amount is far above the NIH adult upper limit for zinc of 40 mg a day.
- Magnesium and melatoninNo spacing rule foundNo official source we checked describes an interaction or a spacing rule between magnesium and melatonin. The NIH magnesium fact sheet does not mention melatonin, and NCCIH's melatonin page does not mention magnesium. NCCIH says people who take medicine should consult their health care providers before using melatonin.
- Magnesium and calciumNo spacing rule foundNo official source we checked gives a spacing rule for magnesium and calcium or says one lowers the other's absorption. The NIH says magnesium helps move calcium across cell membranes. For calcium itself, absorption from supplements is highest with doses of 500 mg or less and is generally greater with food.
Ask your pharmacist first
A medicine is involved, or the timing is a decision for a professional.
Supin schedules what you take around each other
A daily routine by time of day, built from your goals and the bottles you already have, with reminders.
Educational information, not medical advice. Check with your doctor or pharmacist before combining supplements, and always if one of them is a medicine. More on each supplement in the supplement guides.