Fatigue is the most common complaint doctors see in their office. The causes of low energy are numerous, and often there isn’t a single culprit. However, in women of reproductive age, low iron can be a common cause of or contributing factor to low energy. Many of my patients have been told to supplement iron in the past, but they haven’t been told why or for how long. Let’s explore the subject.


When considering any nutrient in the body, we have to think about 3 factors: how much of it are we taking in (diet or supplement), how much of it is getting absorbed in our digestive system, and how much are we losing.

With iron, we know that menstruating women are losing it every month during their period. Women with heavy periods are certainly at risk for iron deficiency and anemia, but even a normal period over time can deplete our iron stores. Regular bleeding can make maintaining iron levels an uphill battle.


Iron intake can also be an issue for women depending on dietary preferences. Iron is highest and most absorbable in animal foods, particularly liver (not exactly a dietary staple). Red meat, dark poultry meats, and shellfish are other good animal sources, although many women restrict these foods for ethical or health reasons. Vegetarian iron rich foods include dark leafy greens, nuts and seeds, legumes, dark chocolate, blackstrap molasses, and fortified grains. However, plant sources of iron can be challenging for our digestive system to absorb.


Iron is a finicky nutrient. It needs certain things to support its absorption, and its absorption can be blocked by common nutrients. To support iron absorption (particularly the harder-to-absorb non-heme iron in plant foods), it is important to have plenty of acid present. Our stomach produces acid when we eat in a relaxed and mindful fashion; eating on-the-go or while stressed can prevent adequate stomach acid. Adding acidity to food (i.e. a squeeze of lemon juice to sautéed kale) can be helpful. Iron supplements generally address this by adding vitamin C (ascorbic acid).


The two peskiest iron inhibitors are calcium and phytic acid. If you are eating a calcium-rich meal (such as one with lots of dairy foods), this is not the ideal time to emphasize iron-rich foods. Same thing goes for supplements; don’t take your calcium and iron supplements together.


Phytic acid is fairly ubiquitous in plant foods and less well-known. You’ll find it in nuts, beans, whole grains, tofu, and more (in other words, healthful foods you are encouraged to eat). It may not be possible to limit or avoid phytic acid in iron-rich meals, so the best that can be done is to utilize cooking strategies that reduce its levels. In particular, soaking, cooking, and fermenting foods rich in phytic acid can help decrease it. Consider doing this with raw nuts, uncooked grains, and dried beans. If you consume soy, consider steering toward tempeh rather than tofu. Tea (green and black) is another major source of phytic acid; avoid drinking tea during an iron-rich meal.


Even with careful intake of iron-rich foods with supportive nutrients and avoidance of absorption inhibitors, some women may still need to supplement. If you’ve had side effects of nausea or constipation with iron in the past, you may need a different form of the mineral. If you’ve taken a supplement in the past without much benefit, the dose may be too low or poorly absorbed. I recommend individualized forms of iron and doses for my patients depending on age, diet, digestive health, and use of other medications and supplements. Repeating lab tests 3 months after initiation of the iron supplement is important to make sure we’re making good progress. During that time, we can work on making the diet more supportive of iron absorption and address heavy menses if needed.


Perhaps you’ve been told in the past that you’re not iron deficient, but it’s important to double check that you’ve been properly worked up. A complete blood count (CBC) alone can be normal (no anemia) even in the presence of iron deficiency, and iron deficiency alone cause symptoms of low energy, hair loss, and poor exercise tolerance. CBC should be checked alongside ferritin, your body’s iron stores.


If you’ve had trouble with low iron and anemia, it may be appropriate to be evaluated for other more serious causes of low iron, including occult bleeds in the digestive system and Celiac disease. Consult your doctor to learn more.