What It Is: Iron is an element that plays a role in the absorption of nutrients, metabolism, and other processes in the body.

How It Works: “Iron is a key component of hemoglobin, a protein in your blood cells that transports oxygen in your blood,” Kristin Gillespie, MS, RD, LDN, a registered dietician at Exercise With Style, tells Bustle. “When your hemoglobin levels are low, which can result from iron deficiency as well as other nutritional or medical causes, you are referred to as being anemic.”

One of the main symptoms of anemia is chronic fatigue. If you’re tired because of an iron deficiency, taking an iron supplement can help.

The Product: NaturesPlus Hema-Plex comes in 85 mg fast-acting softgels. The iron in this supplement is “gentle and non-binding” and is free of allergens like milk, egg, shellfish, peanuts, and soy.

What To Know: Iron supplements are generally well-tolerated, Gillespie says, but they can sometimes cause constipation. As it goes with any supplement, it’s best to check in with your doctor before adding something new to your routine.

What It Is: Vitamin C is a water-soluble vitamin that plays an important role in the production of energy. It’s also an antioxidant that helps boost your immune system.

How It Works: According to Lee, vitamin C supports your adrenal function and decreases high cortisol levels. “The adrenals are responsible for releasing cortisol, so they can help us to manage chronic stress,” she says. What’s more, the adrenal glands have the highest concentration of vitamin C stored in the body, Lee explains. “Because our bodies don't make vitamin C, we rely on our diet or supplements as the source of this nutrient,” she says.

Vitamin C is also required for the body to make stress-response hormones, like epinephrine, norepinephrine, cortisol, and histamine. “Stress can be a root cause of fatigue, and nutrients like vitamin C help support our stress response,” Lee adds.

The Product: Nature’s Bounty Vitamin C comes in 1,000 mg caplets to support your immune system and antioxidant health. It’s made without GMOs, artificial colors, flavors, or sweeteners.

What To Know: Lee recommends taking 2,000 mg of vitamin C a day, preferably with a meal. At higher doses, Lee says it’s possible to develop gastrointestinal side effects like diarrhea. If that happens, go down to 500 mg a day.

What It Is: Vitamin B12 is a water-soluble vitamin that works in just about every body system, says Trista Best, RD, a registered dietitian at Balance One Supplements.

How It Works: Like low iron, low vitamin B12 levels can leave you feeling tired. A deficiency can also lead to a type of anemia known as pernicious anemia, Best says, especially if your diet lacks vitamin B12-rich foods like eggs and dairy products. “Any form of anemia can create chronic fatigue, and supplementing with this vitamin can improve energy levels,” she adds.

The Product: NatureMade Vitamin B12 comes in 1,000 mcg to support energy and your nervous system function. It also helps break down food into energy that your body can use.

What To Know: “If the body doesn't require certain B vitamins, they may be excreted in the urine,” Lee says. And that can make your pee look bright orange or yellow.

What It Is: Vitamin D is a fat-soluble vitamin that plays a role in bone health. It also helps you absorb other nutrients, like calcium and phosphorus.

How It Works: According to Gillespie, vitamin D is a great supplement to take when you need to combat fatigue. She points out that a large portion of the U.S. population is deficient in vitamin D, and that supplementation helps stabilize your levels and treat symptoms of deficiency — including fatigue.

The Product: Garden of Life contains 5,000 IU of fat-soluble vitamin D3, a form of the vitamin that’s easily metabolized. It also contains live probiotics and enzymes to promote absorption.

What To Know: You can take 400 to 800 IU of vitamin D daily, though Gillespie says you may need more during the winter when sunlight (another source of vitamin D) isn’t as available.

There aren’t many side effects associated with vitamin D, but because it is fat-soluble — meaning you don’t pee out the extra like you do with vitamins C and B — it is possible to take too much. “If you are taking a vitamin D supplement regularly, your blood level should be routinely monitored to ensure that dosing is appropriate,” Gillespie adds.

What It Is: Cordyceps is a type of functional mushroom that is thought to give you more energy.

How It Works: “Different types of functional mushrooms have been used for thousands of years and have been shown to help with certain conditions,” says Amy Davis, RD, LDN, a registered dietician with The Balance Dietician. For one, cordyceps may play a role in increasing the body’s production of ATP, aka the energy-carrying molecules within your cells, Davis tells Bustle. “It has also been linked to improving circulation, endurance, and overall vitality,” she adds.

The Product: Om Mushroom Superfood Cordyceps Organic Mushroom Powder comes in a 3.5-ounce pouch with 50 servings of 100% certified organic mushroom cordyceps. Mix it into smoothies, food, or coffee for an energy boost.

What To Know: Davis recommends taking 2 to 3 grams of cordyceps daily. “Side effects are rare, but nausea may occur especially in higher doses,” she says.

What It Is: Ginseng is an adaptogenic herb that is thought to help the body “adapt” or deal with different kinds of stress.

How It Works: Adaptogens like ginseng exert an “anti-fatigue” effect that helps you focus and deal with stress, Lee says. Ginseng works especially well for mental exhaustion, which can leave you feeling drained. “Adaptogens also help the body's resilience in dealing with physical and emotional stresses,” she adds.

The Product: Horbaach’s ginseng capsules contain 1800 mg of the herb per serving, along with flavonoids and ginsenosides, two naturally-occurring antioxidants.

What To Know: Lee recommends checking with your doctor before taking this supplement. “In the case of ginseng, it's not recommended for use for those with kidney failure, who are pregnant, or taking the following medications: anticoagulants, hormone replacement therapy, birth control, or MAO inhibitors,” she says. High doses can also cause breast tenderness and spotting.

What It Is: Magnesium is a nutrient that supports your muscles, nerve function, and energy production.

How It Works: Magnesium deficiency is another common type of nutrient deficiency, says Michael T. Murray, ND, a naturopathic doctor and medical contributor for iHerb. “Boosting magnesium levels will often produce significant improvements in energy levels, especially in those who battle fatigue,” he tells Bustle.

Low magnesium levels can also lead to irritability, muscle cramps, poor sleep quality, and feelings of stress, Murray says. When you take magnesium, it produces a calming effect and also helps you get good sleep. “Poor sleep quality is a big factor for low energy levels in many people,” he says.

The Product: These veggie capsules are formulated with magnesium from magnesium citrate to support energy production. Bluebonnet’s Magnesium Citrate is soy-free, gluten-free, and vegan.

What To Know: “Absorption studies indicate that magnesium is easily absorbed orally,” Murray says. “My recommendation is taking 300 mg of a highly-absorbable form, like magnesium citrate or bisglycinate, at bedtime.”