Feeling wiped out at the end of the day is par for the course for most of us, thanks to logging long hours at the office and juggling overloaded weekend schedules. But if you can’t make it through your to-do list without feeling weak, cloudy-headed or short of breath, your body might be calling out for more than a power nap—you could be iron deficient.MORE: What’s Causing Your Energy Shortage?Whether or not you’re eating animal protein—the most readily absorbable source of iron—it’s a good idea to boost your iron know-how.Iron is a critical nutrient for cell health and overall energy. “In humans, iron is an essential component of proteins involved in oxygen transport,” explains Ruthie Harper, M.D., creator of SkinShift supplements and skincare. Too little iron depletes energy levels and decreases immune function, along with a host of other issues including bruising, hair loss, pale skin, coldness, fast heartbeat, dark circles under the eyes and muscle cramping after exercise.While there’s some debate as to whether vegetarians and vegans are more likely to be low in iron, Ann Louise Gittleman, Ph.D., author of more than 30 books on nutrition, says that women—regardless of whether or not they eat a meat-free diet—are prone to iron deficiency because of menstruation, which depletes them of 15 to 30 milligrams of iron each month.MORE: What To Eat During Your PeriodHow Much Iron Is Enough?The recommended daily intake of iron for adult women ages 19 to 50 is 18 milligrams, more than double that of men, who need only 8 milligrams. To put that in perspective, three ounces of oysters provides about 5.7 milligrams of iron, while one cup of lentils offers 6.6 milligrams of the nutrient. Pregnant women should consume even more daily iron, about 27 milligrams, as their blood has to circulate enough oxygen for themselves and their developing fetus. About half of all pregnant women don’t have enough iron in their bodies, according to the March of Dimes. And that can have health consequences: A 2011 study published in Annals of Allergy, Asthma and Immunology linked anemia—a condition marked by a low count of red blood cells, which can occur from a lack of iron—during pregnancy to an increased incidence of asthma in babies.Many of us believe that our iron intake is adequate, but fail to take into account that we only absorb, at best, about 30 percent of the iron we actually consume. Gittleman and Dr. Harper agree that poor absorption plays a bigger role in iron deficiency than most of us realize. “Many people are highly deficient [in iron] because they do not have enough of certain digestive enzymes, primarily hydrochloric acid, to help them break down the dietary iron and metabolize it and assimilate it properly,” explains Gittleman. “You need to eat more [iron] than your body needs.”What’s more, tannins (found in tea), processed foods and calcium can further decrease absorption of iron. Of course, we don’t recommend skipping your daily calcium supplements but rather taking them with meals that don’t also include iron-rich foods.So where does that leave women, especially non-meat eaters, who want to avoid a low iron slump? The solution isn’t simply to grab a bottle of iron supplements on your next trip to the health food store. That’s because there’s a chance your iron stores could become too high, which can lead to serious toxicity and liver damage.MORE: 10 Myths About Vitamin SupplementsThe Best Sources of IronIf you suspect that you may be low in iron, the first step is to get a blood test from your doctor, which will determine if you need to increase your intake of iron-rich foods, take a supplement or both. “If you are slightly low in iron, often times foods high in iron are your best option for replacing your iron needs,” says Harper. “We cannot do better than nature, and food provides a natural source of iron along with nutrients that can maximize iron absorption.”For vegetarians and vegans, getting enough dietary iron takes some monitoring, as iron from plant sources (called non-heme) is less absorbable than iron from animal sources (heme). Some of the best vegan and vegetarian sources of iron are lentils, kidney beans, fortified cereals, leafy greens such as spinach, spirulina, quinoa and soybeans. And the most iron-packed fresh fruit? Watermelon. However, both beans and whole grains contain phytates, antioxidant compounds that block iron absorption. To decrease the phytates in your grains and beans, soak them overnight and drain before cooking.To get the most iron from your meals, try remembering one basic food pairing: iron and vitamin C. Eat a vitamin C-rich food or take a C supplement when you consume iron—this can be as unfussy as a dash of citrus-based dressing on a green salad, says Gittleman—and you’ll boost iron absorption. Nutritionist Haylie Pomroy recommends that vegetarians and vegans seek out iron-rich blackstrap molasses, drink ‘iron-building’ alfalfa tea, take a B vitamin-rich supplement and cook and reheat food in an iron skillet, which also contributes a small dose of iron to food.MORE: How to Build a Beautiful Superfoods SaladWhen dietary iron isn’t enough, talk to your doctor about a supplement. But be aware: The most commonly used iron supplement, ferrous sulfate, is the most apt to cause gastrointestinal upset and constipation, notes Harper. Don’t be alarmed if you’re instructed to take iron supplement doses as high as 300 milligrams, according to Harper, as they commonly only contain about 50 milligrams of absorbable iron. Gittleman has helped her vegetarian and vegan clients boost their iron levels with herbal iron supplements (they often come in liquid form, with names like Floradix), which contain iron-rich herbs such as yellow dock root and dandelion root. A big plus for these herbal supplements is that they’re also non-constipating. Skip liquid sources of heme iron, which have the unpleasant side effect of darkening your teeth.While keeping your iron levels in check may involve a little more mealtime mindfulness than you’re used to, the fatigue and health complications you’ll avoid are significant, especially for women. And we need all of the energy we can get.QUIZ: Find Out How What Your Eat Affects Your Beauty