#1: Your hair's seen better days...

The best way to get all your necessary vitamins, minerals, and antioxidants is by eating a nutritious diet (duh)—but that’s easier said than done. In fact, a recent report from the Centers for Disease Control and Prevention (CDC) found that one in 10 people have at least one vitamin deficiency.

So should you be taking a supplement to make up for that lack? The answer is tricky. “It can be completely confusing to determine which vitamins you should or shouldn’t be taking,” says Sherry Ross, M.D., an ob-gyn and women’s health expert at Providence Saint John’s Health Center in Santa Monica.

Of course, the best thing to do is speak with your healthcare provider before adding any supplement to your routine. But here are some key signs that could indicate you’re short on a specific nutrient or two. 

Your Hair and Nails are Weak

You could be deficient in: biotin

It’s found in: whole grains, eggs, dairy, nuts, and proteins like salmon and chicken

Here's the deal: If you’re experiencing skin inflammation, irritation, or flaking or notice that your hair is feeling thinner, more lackluster, and brittle, you may not be getting enough biotin. (Another key sign is weak and brittle nails.)

Recommended daily dosage (through diet and/or supplement): 30 micrograms per day

Your Pooping Habits Have Changed

You could be deficient in: niacin

It’s found in: meat, fish, eggs, nuts, green veggies, and enriched breads and cerals

Here's the deal: Pellagra, or niacin deficiency, can cause serious and rather unappealing side effects. Those range from bodily lesions that worsen in direct sunlight to gastrointestinal symptoms like constipation, diarrhea, nausea, and vomiting. “Niacin plays some major roles in helping our bodies function properly,” says Kristine Arthur, M.D., an internist at Orange Coast Memorial Medical Center in Fountain Valley, California. “It can boost good cholesterol and lower bad cholesterol, help reduce hardening of the arteries, and produces certain hormones in the adrenal glands that help remove harmful chemicals from the liver.”

Recommended daily dosage (through diet and/or supplement): 14 to 18 milligrams 

You're Pregnant

You need more: folate

It’s found in: dark green veggies (like spinach), chickpeas, and lentils

Here's the deal: The majority of people get enough folate through their diet, says Ross, but pregnant women need to take a folic acid (the synthetic form of folate) supplement regardless. That's because not getting enough of the stuff can lead to major issues for your baby. According to the CDC, folate helps prevent neural tube defects of the spinal cord and brain. 

Recommended daily dosage (through diet and/or supplement): 400 micrograms, but you’ll need to ask your M.D. how much you should be taking each day to meet that goal

You Bruise Easily

You could be deficient in: vitamin C

It’s found in: citrus fruits, papaya, yellow bellow peppers, guava, kale, and strawberries

Here's the deal: Your mom’s been telling you forever to make sure you drink your share of OJ—and she’s onto something. Because vitamin C is not naturally produced within the body, it’s surprisingly common for people to experience a deficiency. “Vitamin C is a vital antioxidant that helps protect cells from damage caused by free radicals we’re exposed to in the environment such as air pollution, cigarette smoke, and ultraviolet light from the sun,” says Ross. “It also helps the immune system work well in order to protect the body from diseases.” When you’re running really low, you might notice increased bruising or unexplained red or purple marks. “This is likely due to the weakened blood vessels near the skin’s surface that break and leak red blood cells,” explains Ross.

Recommended daily dosage (through diet and/or supplement): 60 milligrams

Your Eyes are Bloodshot

You could be deficient in: vitamin B2

It’s found in: milk, meat, eggs, nuts, fish, and green, leafy vegetables

Here's the deal: Those running low on vitamin B2, a.k.a. riboflavin, often show very visible signs (like bloodshot eyes). “This type of deficiency is more common in people on extreme diets who are underweight or those with digestive problems such as celiac disease,” says Arthur. The body needs riboflavin for growth and overall good health and to breakdown carbohydrates, proteins, and fat.

Recommended daily dosage (through diet and/or supplement): 1.2 milligrams

You Feel Unusually Fatigued

You could be deficient in: calcium

It’s found in: dairy products like milk and yogurt, dark greens, almonds, and chickpeas

Here's the deal: If you’re falling short, your bones will start to deteriorate and you’ll experience low energy, say experts.

Recommended daily dosage (through diet and/or supplement): “While current recommendations are to get as much calcium as possible via your diet, you can supplement in limited amounts if you’re not getting your recommended daily allowance of 1,000 milligrams a day for women ages 50 and younger and 1,200 milligrams for women over 50,” says Arielle Levitan, M.D., co-founder of Vous Vitamin and author of The Vitamin Solution: Two Doctors Clear the Confusion About Vitamins and Your Health.

You Get Leg Cramps

You could be deficient in: vitamin E

It’s found in: nuts, seeds, vegetable oils, green leafy vegetables, eggs, and fortified cereals

Here's the deal: Vitamin E is one of the most fundamental vitamins our body craves, as one of its main jobs is to slow down the aging process. “While a vitamin E deficiency is rare, it can occur in people who have underlying problems with fat absorption, like those with Crohn’s disease, cystic fibrosis, malnutrition, very low-fat diets, or genetic conditions affecting fat absorption,” says Ross. One study published in the journal California Medicine connected a vitamin E deficiency to leg cramps. “The research found that severe nocturnal leg cramps and restless leg syndrome actually went away when patients were given adequate doses of vitamin E,” says Ross.

Recommended daily dosage (through diet and/or supplement): 15 milligrams