Iron Deficiency in Women: Symptoms, Causes, and the Best Supplement Forms

Choosing the right iron supplement can mean the difference between effective correction and weeks of stomach discomfort:

• Iron bisglycinate (chelated iron): This is increasingly the preferred form among nutritionists. It is gentle on the stomach, well-absorbed, and less likely to cause the constipation and nausea associated with other forms. Absorption is less affected by food and other minerals.
• Ferrous fumarate: Contains a higher percentage of elemental iron (33%) and is reasonably well-tolerated. A good mid-range option.
• Ferrous sulphate: The most commonly prescribed form and the cheapest. However, it has the highest rate of gastrointestinal side effects including constipation, nausea, and dark stools.
• Look for added vitamin C: Vitamin C can increase iron absorption by up to 6x. A supplement that includes it saves you having to coordinate timing with orange juice.
• Avoid combined multivitamins for iron correction: If you have been diagnosed with iron deficiency, a standalone iron supplement will be more effective than a multivitamin, which typically contains only maintenance-level doses.

Iron supplementation may be particularly important for:

• Women with heavy menstrual periods — the most common cause of iron deficiency in premenopausal women
• Pregnant women, especially in the second and third trimesters when blood volume increases dramatically
• Vegetarians and vegans — plant-based (non-haem) iron is absorbed at only 2–20% compared to 15–35% for animal-based (haem) iron
• Endurance athletes, particularly female runners (repetitive foot striking can damage red blood cells)
• Regular blood donors — each donation removes approximately 250mg of iron from your body
• People with coeliac disease, IBD, or other conditions affecting nutrient absorption

Always confirm deficiency with a blood test before supplementing. Excess iron is stored in the body and can cause harm at high levels.

Take your iron supplement with vitamin C-rich foods or drinks (orange juice, strawberries, bell peppers) to dramatically boost absorption. Avoid taking iron within 2 hours of calcium supplements, dairy products, tea, or coffee — all of which inhibit iron absorption. If your supplement causes stomach upset, try taking it every other day instead of daily — research from ETH Zurich found that alternate-day dosing actually improved absorption while reducing side effects. Cook in cast-iron pans to add small amounts of dietary iron to your food. Pair plant-based iron sources (lentils, spinach, beans) with vitamin C at the same meal.