Supplements are big business, but there's debate over whether they actually improve your health.

News flash number one: Vitamin and mineral supplements—which nearly half of Americans down daily—don't deliver on health-revving promises, per a recent study in Annals of Internal Medicine. News flash number two: Nearly 90 percent of Americans don't get enough nutrients like vitamins D or E through food alone, so supplements are everyone's best bet, according to new research in Nutrients. Wait...what?!

Here's the truth: Your every cell needs nutrients to function, and it's better to get those through foods such as leafy greens, whole grains, and fatty acid-rich fish. But yeah, we live in the real world—and it's not all salads and sushi, says Denise Londergan, R.D., M.P.H., of the Ohio State University Wexner Medical Center. Greasy takeout happens; so do nutrient gaps that can put your well-being at risk.

A multivitamin might cover some of your bases, but depending on your lifestyle, it's probably not enough, says nutritional-medicine expert Christine Wood, M.D. Read on—then talk to your doc—for the vita-mix that's right for you.

What You Should Pop

Your ideal nutritional blueprint is as unique as your DNA. Sure, it depends on your body chemistry, but also on how often you hit the gym, which foods you won't eat, even where you live. Follow these guidelines—based on which type(s) of lifestyle you most closely follow—to help fuel your body and mind.

The Fitness Buff

Working out for more than 1.5 hours at a time depletes your nutrient stash.

You Might Be Missing: Iron. It's found mainly in meats and beans, and you need at least 18 milligrams per day of this micro mineral that helps transport oxygen to cells. Low levels can sap your energy and lead to headaches.

Find It In Food... Three-fourths of a cup of fortified cereal has a day's worth. A cup of soybeans has 8.8 milligrams; a cup of lentils has 6.6 milligrams.

...Or A Supp Always first consider your diet (and buy gut-friendly "elemental iron"), because too much can lead to constipation.

The Desk Jockey

This means you, cube dwellers. But also pay heed if you live north of Atlanta.

You Might Be Missing: Vitamin D. Hard to find in foods, it's also produced naturally in the body when sunlight hits your skin (so colder northern climates could mean less D). Getting 600+ IU per day can help the body fight infections, build strong bones, and prevent depression.

Find It In Food... A three-ounce serving of salmon has 447 IU; one cup of milk has up to 124 IU; one egg has 41 IU (the D is in the yolk).

...Or A Supp Food alone won't help the D-deficient. Look for easy-to-absorb daily D3 cholecalciferol supplements of up to 2,000 daily IU.

The Vegetarian

Congrats—produce is loaded with nutrients! Except for one biggie.

You Might Be Missing: Vitamin B12. Virtually nonexistent in plant foods, it keeps blood and nerve cells healthy and can help protect your brain and muscles. Not getting the recommended 2.4 micrograms per day could leave you feeling weak and tired. (This goes for you, too, vegans.)

Find It In Food... Dairy foods and eggs contain a bit of B12; fortified soy products or breakfast cereal can give you your full daily value.

...Or A Supp Don't do animal, dairy, or processed eats? Look for a daily methylcobalamin tablet (it's the active form of B12).

The Future Mom

Kids on your "someday" list? You can prep for a drama-free pregnancy (yes, even one that's years away).

You Might Be Missing: Folate. Mostly found in leafy greens, this B vitamin helps shield against neural tube defects (i.e., complicated brain and spine birth defects). You should get 400 to 800 micrograms every day.

Find It In Food... Like we said: leafy greens. Load up on 'em. A half-cup of cooked spinach packs 131 micrograms; a cup of shredded romaine has 60 micrograms.

...Or A Supp Most experts say you should supplement. Look for 5-methyl-tetra-hydrofolate or L-methylfolate on the label.

The Gluten-Free Gal

If you're off wheat, you could be missing some key nutrients.

You Might Be Missing: Magnesium. Whole grains are packed with the mineral, which is important for bone and heart health. Up to 320 milligrams per day also helps your body absorb calcium and potassium, regulate blood sugar, and control blood pressure.

Find It In Food... A half-cup of edamame has 50 milligrams; a half-cup of black beans packs 60 milligrams; a baked potato provides 40 milligrams.

...Or A Supp If you skip all wheat, rice, and fortified cereals, look for a daily magnesium citrate supplement.