Heavy periods, iron pills and your gut: common questions answered

Perimenopause doesn't always mean lighter periods. For some women it brings longer or heavier bleeding, a blood test showing low iron and a recommendation to start iron supplements. Then the stomach trouble begins.

If that sounds familiar, here are answers to the questions that come up most often, including what research says about making iron easier on your gut.

Are heavier or longer periods normal in perimenopause?

They're common. In the Study of Women's Health Across the Nation, 1,320 midlife women recorded their bleeding on daily calendars for up to 10 years. At least three periods lasting 10 days or more were reported by 77.7% of women, at least three stretches of spotting lasting 6 days or more by 66.8%, and at least three episodes of heavy bleeding lasting 3 days or more by 34.5%. These patterns were linked to the stage of the menopause transition, uterine fibroids, hormone use and ethnicity, and heavy bleeding was also linked to body mass index (Paramsothy et al., 2014).

Common isn't the same as harmless. Bleeding that soaks through a pad or tampon every hour or two, periods that come much closer together than usual, bleeding between periods or any bleeding after menopause deserve a medical evaluation.

Why do iron pills upset my stomach?

Digestive side effects from iron are well documented. A meta-analysis of 43 randomized trials with 6,831 adults looked at ferrous sulfate, the standard form of oral iron. It more than doubled the odds of gastrointestinal side effects compared with placebo (odds ratio 2.32), and raised them about threefold compared with intravenous iron (odds ratio 3.05). The analysis didn't find a clear link between the dose and the likelihood of side effects (Tolkien et al., 2015).

Is one type of iron gentler than another?

Possibly, but the evidence is hard to compare. A systematic review of 111 studies with 10,695 patients found that reported rates of digestive side effects varied by product: for example, 43.4% for ferrous fumarate, 30.2% for standard ferrous sulfate, 29.9% for ferrous gluconate and 18.5% for ferrous glycine sulfate. One extended-release ferrous sulfate product had the lowest rate. The authors noted that the included studies differed considerably in design, which limits direct comparisons (Cancelo-Hidalgo et al., 2013).

Different forms also contain different amounts of actual, or elemental, iron per tablet. So don't switch products on your own. Ask your doctor or pharmacist to help you find an equivalent option.

Do I really need to take it every day?

Not necessarily, and this is one of the more practical findings in iron research. A dose of oral iron raises a hormone called hepcidin for about 24 hours, which reduces how much iron you absorb from a dose taken later that day or the next day (Stoffel et al., 2020).

In a trial of iron-depleted women aged 18 to 40, taking 60 mg of iron on alternate days for 28 days led to more total iron absorbed than taking the same dose every day for 14 days: 175 mg vs. 131 mg from the same number of doses. Splitting a larger dose into two doses on the same day didn't improve absorption (Stoffel et al., 2017). A follow-up study in 19 women with iron-deficiency anemia found that absorption was 40 to 50% higher from doses that didn't follow another dose the day before (Stoffel et al., 2020).

These studies measured absorption, not stomach comfort, and they were done in younger women. Still, fewer doses per week may mean fewer days with side effects. Ask your doctor whether an alternate-day schedule fits your situation.

What else can make iron easier on my gut?

• Track your symptoms for the first two weeks, including stool changes, nausea and bloating, so you have specifics to discuss.
• Ask about timing. Your pharmacist can help you balance absorption and comfort, including whether to take iron with food and how to space it from calcium, antacids or other supplements.
• Stay ahead of constipation. If stools start getting harder, bring it up early rather than waiting weeks.
• Don't stop on your own. If side effects are hard to live with, tell your doctor. There are other forms, other schedules and, for some people, intravenous iron.

When is low iron a gut question, not a period question?

Heavy periods can explain low iron, but they're not the only possible cause. Ask your doctor whether you need a digestive evaluation if:

• You have iron deficiency or anemia after menopause
• Your iron stays low despite treatment, or your bleeding doesn't seem to explain how low it is
• You notice blood in your stool or black, tarry stools (iron can darken stool, so mention it if you're unsure)
• You have unexplained weight loss, ongoing diarrhea or bloating
• You have a family history of celiac disease or colon cancer, or you're 45 or older and haven't had colorectal cancer screening

For a broader look at digestive changes in this decade, here's what changes in the gut after 40.

Sources

1. Paramsothy P, Harlow SD, Greendale GA, et al. Bleeding patterns during the menopausal transition in the multi-ethnic Study of Women's Health Across the Nation (SWAN): a prospective cohort study. BJOG. 2014;121(12):1564-73. PMID 24735184
2. Tolkien Z, Stecher L, Mander AP, Pereira DI, Powell JJ. Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLoS One. 2015;10(2):e0117383. PMID 25700159
3. Cancelo-Hidalgo MJ, Castelo-Branco C, Palacios S, et al. Tolerability of different oral iron supplements: a systematic review. Curr Med Res Opin. 2013;29(4):291-303. PMID 23252877
4. Stoffel NU, Cercamondi CI, Brittenham G, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. Lancet Haematol. 2017;4(11):e524-e533. PMID 29032957
5. Stoffel NU, Zeder C, Brittenham GM, Moretti D, Zimmermann MB. Iron absorption from supplements is greater with alternate day than with consecutive day dosing in iron-deficient anemic women. Haematologica. 2020;105(5):1232-1239. PMID 31413088

This article is for general information and isn't medical advice. Don't start, stop or change an iron supplement without talking to your healthcare provider, and seek care promptly for very heavy bleeding or any bleeding after menopause.