How to Take Iron Supplements to Maximize Absorption

Iron is crucial for individuals leading active lifestyles

Ashley Reaver
By Ashley Reaver
Jovan Mijailovic
Edited by Jovan Mijailovic

Updated January 12, 2024.

a person holding a bowl of salad rich in iron with oranges, nuts, and radishes

Iron is an incredibly important mineral for health. Not only is it a crucial component for many biochemical reactions in our bodies, but it is also required for proper oxygen transport.

When our iron levels drop, it can leave us feeling sluggish and depleted. Fortunately, iron supplements can help restore our vitality. But, to harness the full benefits of these supplements, it's crucial to understand how to take iron supplements and when to take them.

Knowing your iron biomarker levels is especially important for athletes, active premenopausal females, those fighting fatigue, frequent blood donors, and anyone generally interested in their health. So, let's break down the best ways to supplement iron to achieve maximum absorption.

» Learn more about how inflammation affects your iron levels

Why are athletes at risk for under-optimized iron?

While iron is an essential nutrient for everyone, active individuals have higher needs as there is a higher rate of red blood cell (the oxygen transporter) destruction associated with activity. Additionally, many athletes are overly health conscious and may steer away from high-iron foods, like beef, for health reasons, which can lead to inadequate intake.

» Find out how monitoring iron status can save your season

What you need to know about iron absorption

Like with most biomarkers, the law of diminishing returns applies to your iron markers, too. Simply put, those who have the most room to improve will improve the most. As iron levels increase, it becomes more difficult to get smaller improvements.

In general, iron absorption falls from about 20% to 10% as ferritin increases from 15 to 60 mg/dL. [1] Keep at it! Improving ferritin is like filling a swimming pool with a garden hose (unless it is falsely high from inflammation, of course). Choosing high-quality sources of iron and being strategic with supplementation is important.

Did you know that iron intake is especially important for women?

In our healthy, active population, low ferritin levels are fairly common, especially among premenopausal females. Of our users, 50% of females under the age of 50 have suboptimal ferritin levels.

a pie chart showing the percentage of ferritin levels of InsideTracker females under the age of 50

Whereas men typically store around 600-1,000 mg of iron at a time, women only store 200-300 mg. [2] Blood loss from menstruation depletes women's iron stores more quickly, and heavy bleeding during periods is associated with an increased risk for iron deficiency. [3] So it's especially important for women to focus on optimizing iron intake to maintain their body's iron stores and to replenish lost iron from monthly cycles.

Strategies to optimize iron intake

Iron supplements or iron-rich meals are best absorbed when they are not taken before or after exercise.

In theory, recovering from a hard run with a steak dinner makes sense since the body certainly needs to replenish some iron stores; however, since inflammation peaks post-workout, it is unlikely that we are going to absorb a fair amount of that iron, thus, wasting a steak dinner! Enjoy your lean cuts of beef on easier workout days.

Other good sources of iron include shellfish, beans, dark chocolate (check the labels), fortified cereals, and dark leafy greens (best absorbed when eaten with a squeeze of citrus).

How to take iron supplements

  • Take your supplement before bed: This is likely to be the easiest time to have an empty stomach. Cutting off your food intake two hours before bed will also have other benefits.
  • Have a large breakfast or lunch: Cut out your usual snack by eating more in one sitting. Small salads for lunch may sound like a good idea, but if they result in you reaching for a less-than-stellar snack three hours later, you didn’t eat enough. Go for more calories at meal times to stave off hunger for four hours.
  • If you need food, plan to eat a piece of fruit with your supplement: Citrus and bell peppers are winners for their high vitamin C content, which helps improve absorption, and they are also relatively low in fiber. Berries are also a good source of vitamin C, but their fiber content can decrease iron absorption.

When is the best time to take iron supplements?

The ideal time for taking an iron supplement is one hour before a meal or two hours after to ensure an empty stomach.

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It is possible to take too much iron!

Finally, and something that's seen quite often, is taking too much iron at one time. Clinically high levels of serum iron, while you are supplementing can mean that you are taking too much iron at once, and your system can’t do much with it.

If you have high serum iron and a low ferritin level, consider breaking up your supplement into smaller doses throughout the day. A mega dose of 65mg, which should only be taken if prescribed by your physician, is unlikely to be well absorbed.

Try starting at 14mg once per day and increasing to 14mg twice per day if your biomarkers are not improving (ferrous sulfate is our recommended form of iron supplement). It's also important to alert your physician to your iron levels and supplementation in case your low ferritin levels indicate something more serious.