Calcium supplements are generally safe, recommended for older women, and are not likely to directly affect your blood pressure. They may, however, indirectly cause your blood pressure to increase if you are currently being treated for existing hypertension.
Calcium supplements can interfere with the action of certain high blood pressure medications, making them less effective at controlling blood pressure. In this case, the calcium isn’t actually causing your blood pressure to rise, but rather stopping your medications from exerting their blood pressure lowering effects.
These interactions are uncommon, and only affect a limited number of high blood pressure medicines, mainly thiazide diuretics and calcium channel blockers. Taking calcium supplements while using a thiazide diuretic can disrupt the ability of the diuretic to act on the kidneys, decreasing the drug’s effectiveness as an anti-hypertension agent.
In some cases, taking calcium while using a thiazide diuretic can lead to a condition called milk-alkali syndrome. In this syndrome, an interaction between the calcium and diuretic causes the body to become less acidic than normal and dramatically raises the amount of calcium present in the blood. Along with blood pressure effects, milk-alkali syndrome can cause serious problems like heart attack, acute kidney failure, and seizure.
If you use a thiazide diuretic, you should limit your intake of calcium to less than 1,500mg per day.
Calcium channel blockers can also be affected by calcium supplements, but typically only at high levels associated with intravenous calcium administration (which can occur in certain hospital settings). In this case, the interaction is very straight forward – calcium channel blockers are designed to stop calcium from interacting with blood vessels, which lowers the blood vessel’s ability to tighten and ultimately leads to looser vessels and lower blood pressure. Very high levels of blood calcium can “out-compete” the drug’s ability to block this interaction, since there is so much calcium that the drug simply cannot block it all. When this occurs, it is easily recognized and can be quickly reversed by stopping the administration of calcium.
Calcium supplements do not interfere with other common blood pressure medications like ACE inhibitors, beta blockers, or other types of diuretics. Still, you should always consult your doctor before beginning supplementation with any vitamin, mineral, or herbal product.