Constipation from supplements is a real and common problem. Iron is the worst offender, followed by calcium. The good news: form matters, and there are workarounds.
The Main Culprits
Iron - The #1 supplement cause of constipation - Ferrous sulfate is the worst (but cheapest) - Iron bisglycinate is gentler - Higher doses = more constipation - Also causes nausea in many people
Calcium - Common constipator - Calcium carbonate is most constipating - Calcium citrate is gentler (and absorbs better without food) - Large doses worsen the effect
Aluminum-containing antacids - If you count these - Regular use definitely slows things down
Why They Cause Constipation
Iron: Unabsorbed iron irritates the gut lining and changes gut bacteria composition. It also has an astringent effect on intestinal tissue.
Calcium: Competes with magnesium for absorption. Low magnesium = slower bowel motility. Calcium also has a muscle-relaxing effect on the intestines.
Solutions That Work
Switch forms: - Iron bisglycinate instead of ferrous sulfate - Calcium citrate instead of carbonate
Add magnesium: - Magnesium citrate actively promotes bowel movements - 200-400mg at bedtime often solves the problem - Bonus: most people need more magnesium anyway
Lower doses, more frequency: - 25mg iron 2x daily may work better than 50mg 1x daily - Same total, less GI stress
Take with vitamin C: - Improves iron absorption so more goes into your blood, less stays in your gut
Increase fiber and water: - Basic, but it helps offset the effect