You’re planning a backpacking trip to the mountains – great! Creating a safe and successful trip involves preparing maps, routes, gear, first-aid supplies, and numerous other tasks. Chances are, if you live at low elevation, you want to minimize the risk that altitude illness will affect your trip. You’ve probably considered this with route planning and have possibly considered taking medication to help alleviate the effects of altitude. Did you know that your nutrition can play a role as well?

First, a little physiology reminder. As we ascend, our bodies undergo multiple adaptations to acclimatize to altitude. At altitude, the partial pressure of oxygen is lower, which decreases the oxygen exchange from our lungs into the blood. This, of course, can contribute to decreased exercise performance and altitude illness, with symptoms such as headache, fatigue, and shortness of breath. Our bodies adapt by concentrating the blood we have, and by producing new red blood cells.

Iron is a necessary mineral for production of red blood cells. Lack of iron therefore limits the adaptation of red blood cells to altitude, contributing to altitude sickness. Researchers have studied this phenomenon in athletes and military recruits, and have come up with some recommendations. A good review article from 2019 summarizes these in more detail than described below (but does not substitute for advice from your own physician).

Do I need an iron supplement for traveling to altitude? Here are the basics:

1. Before going to altitude, know your serum ferritin.

Ferritin measures the body’s iron stores in the tissues, rather than in the blood, and is a more sensitive test for iron deficiency than hemoglobin or hematocrit. Make an appointment with your doctor, and request to have this checked 4-6 weeks before your trip.

a. If ferritin is < 35ng/mL, consult a physician and consider taking 100mg elemental (see below) iron as a single daily dose.

b. If ferritin is <15ng/mL, consult a physician.

2. Iron supplementation while at altitude is even more important than beefing up beforehand.

a. If ferritin was <100ng/mL, about a week before the trip consider adding / increasing supplement to 200mg elemental iron as a single daily dose, and continue this during the trip.

b. If ferritin was between 100 and 130ng/mL, about a week before the trip consider taking 100mg elemental iron as a single daily dose, and continue this during the trip.

c. If ferritin was >130ng/mL, a supplement may not be needed.

Which kind of iron should I take?

The recommended amounts of iron above are elemental iron. This may not be the number that’s on your bottle. For example, Ferrous Sulfate 325mg, the most common form of iron supplement, contains 65mg of elemental iron. Assistance with other conversions may be found here.

Is an iron supplement going to bother my stomach?

Nausea and constipation are unfortunately side effects from iron in some people. If this happens, try lowering the dose, taking the supplement with food, or using a daily stool softener (such as docusate sodium) along with the iron. Occasionally dark stools may occur as a result of iron supplementation. As long as this occurs only after starting an iron supplement, without a tarry or bloody look to the stool, it is not worrisome.

Can my iron level get too high from taking a supplement?

Yes. Iron toxicity is rare but possible in otherwise healthy individuals.

I heard I need to take vitamin C with iron?

While vitamin C does improve the absorption of iron, taking them together is not strictly necessary.

I’m planning an extended thru-hike. For how long do I need to continue the iron supplement?

As many of the studies on iron and altitude have been conducted at short-term athletic training camps, this is unclear. If the body is fully altitude acclimatized and the ferritin level is normal, food sources may be adequate.

What about food? Can I just get iron in my food?

Certainly this is possible, though if your iron stores are low, you either have not been getting enough, or may have a medical condition which is causing the low iron. Your physician can help you determine the cause and choose the best course of action. If more dietary iron is needed, trying to replete an iron deficiency with 100mg/day from regular food sources would be particularly difficult. The NIH has an Iron Fact Sheet for Health Professionals that discusses the USDA recommended daily allowance for iron. This is 18 mg daily for women aged 19 – 50 and 8mg for women over 50 and for men.

Below is a chart of iron content in common foods. We tend to think of iron being present in red meat, but ½ cup of chickpeas or kidney beans has roughly the same amount of iron as 3oz of red meat. For backpacking, a quick internet review of the nutrition information of a popular brand of dehydrated meals (with meat) shows only 1-3mg of iron per serving. Interestingly, inspection of some vegetarian dehydrated meals in my own pantry show 4-7mg of iron per serving.