Calcium supplements and your gut: a checklist for women over 45

Started a calcium supplement and suddenly feel backed up or bloated? You're not imagining the connection. Calcium tends to come up as bone health becomes a bigger topic around menopause, and it's also a supplement with a well-documented tendency to upset the gut.

This checklist walks through whether you need one, how to choose a form, and how to take it in a way that's easier on your digestion.

First, why calcium can bother your gut

Researchers pooled side-effect data from seven randomized trials of calcium supplements. Digestive complaints, including constipation, cramping, bloating, upper abdominal symptoms and diarrhea, were reported by 14.1% of people taking calcium compared with 10.0% of people taking a placebo. In one of the trials, hospital admissions for functional digestive problems were 6.8% with calcium vs. 3.6% with placebo (Lewis et al., 2012).

That's not a reason to skip calcium you need. It's a reason to be deliberate about whether you take it, which form you choose and how you take it.

Checklist: before you buy

• Tally what you already get from food. Dairy, fortified plant milks, canned fish with soft bones, tofu made with calcium and some leafy greens all count. A supplement is meant to fill a gap, not double up on what your diet already covers.
• Ask your doctor whether you need a supplement, and how much. In the Women's Health Initiative, 36,282 postmenopausal women aged 50 to 79 took 1,000 mg of calcium (as calcium carbonate) plus 400 IU of vitamin D daily, or a placebo, and were followed for an average of seven years. The supplement group had 1.06% higher hip bone density but no significant reduction in hip fractures overall. When the analysis focused on women who kept taking their pills, hip fracture risk was lower (Jackson et al., 2006).
• Mention any history of kidney stones. In that same trial, the supplement group had a higher risk of kidney stones (hazard ratio 1.17), so it's worth raising before you start (Jackson et al., 2006).

Checklist: choosing a form

• Know the two main options. Calcium carbonate and calcium citrate are the most common forms. In a study of 24 postmenopausal women, marketed carbonate and citrate products were absorbed equally well, and carbonate was the less expensive choice (Heaney et al., 2001).
• Take carbonate with food. In people with very low stomach acid, carbonate taken on an empty stomach was poorly absorbed: about 4% of the dose, compared with about 45% for citrate. When the same people took carbonate with a normal breakfast, absorption was completely normal (Recker, 1985).
• Consider citrate if meals don't fit your routine. If you often take supplements between meals, or you use medication that lowers stomach acid, ask your pharmacist whether citrate makes more sense for you.

Checklist: how you take it

• Split larger amounts. In healthy women eating a meal, the share of calcium absorbed dropped as the dose went up, from about 64% at the smallest amounts tested to 28.6% at 500 mg (Heaney et al., 1990). Two smaller doses at different meals tend to be absorbed more efficiently than one large dose.
• Change one thing at a time. If you're also starting vitamin D, magnesium or a new fiber, stagger them by a week or two so you can tell what's causing what.
• Track your gut for two weeks. Note how often you go, whether stools are hard or soft, and your afternoon bloating on a 0 to 10 scale.
• Keep everything else steady. Same water intake, same fiber, same meals where possible, so you're comparing like with like.

Checklist: if your gut still complains

• Try a smaller dose split across two meals
• Ask your pharmacist about switching forms, for example from carbonate to citrate
• Shift more of your calcium to food sources, if your doctor agrees
• Recheck whether your total daily amount is still the right one for you
• If constipation persists, work on it directly rather than simply putting up with it

When to call your doctor

Check in with your doctor if you have severe or lasting constipation, abdominal pain that doesn't settle, blood in your stool, or strong pain in your side or back that could signal a kidney stone. And if constipation or bloating started before the calcium, or continues after you stop it, look beyond the supplement. Here's a look at other reasons digestion changes after 40.

Sources

1. Lewis JR, Zhu K, Prince RL. Adverse events from calcium supplementation: relationship to errors in myocardial infarction self-reporting in randomized controlled trials of calcium supplementation. J Bone Miner Res. 2012;27(3):719-22. PMID 22139587
2. Jackson RD, LaCroix AZ, Gass M, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354(7):669-83. PMID 16481635
3. Heaney RP, Dowell MS, Bierman J, Hale CA, Bendich A. Absorbability and cost effectiveness in calcium supplementation. J Am Coll Nutr. 2001;20(3):239-46. PMID 11444420
4. Recker RR. Calcium absorption and achlorhydria. N Engl J Med. 1985;313(2):70-3. PMID 4000241
5. Heaney RP, Weaver CM, Fitzsimmons ML. Influence of calcium load on absorption fraction. J Bone Miner Res. 1990;5(11):1135-8. PMID 2270776

This article is for general information and isn't medical advice. Talk to your healthcare provider or pharmacist before starting or changing calcium or vitamin D, especially if you have kidney problems or take other medications.