Every cell in your body needs B vitamins, a family of eight nutrients necessary for cell metabolism. A few of their headliner jobs: producing and regulating DNA and RNA (the body’s genetic material), turning food into energy, enabling nerve function, and equipping cells to divide and make new cells.

The B vitamins are not all found in the same foods, but some of the most common sources are dark leafy greens, meats, poultry, whole grains, dairy products, eggs, fish and seafood, and nuts and seeds. Because the Bs are widely spread across many food groups, most Americans get enough B vitamins in their diet.

Even so, it’s possible for people to have below-optimum levels, especially of B12, for two main reasons: 1. B12 is found only in animal sources (including eggs, fish and dairy), so vegans must rely on supplements (which use a synthetic form) to get enough; and 2. People ages 50 and older have a hard time absorbing it from food. “It’s recommended that people over 50 obtain most of their B12 from fortified foods or dietary supplements, because our bodies absorb the synthetic form better than the natural one,” says Carol Haggans, R.D., a consultant for the National Institutes of Health Office of Dietary Supplements.

To get better acquainted with the B family and see if you’re a good candidate for a supplement, check out this quick primer. Pay special attention to B6, B9 and B12—the ones you’re most likely to need in supplement form.

Meet the B Family

B1 – thiamine

Also spelled thiamin, this vitamin helps keep your heart, mind and eyes working properly. It helps metabolize carbs, protein and fatty acids; supports RNA and DNA production; and assists nerve function. Three ounces of pork delivers nearly 75 percent of your RDA; half a cup of green peas provides almost 20 percent.

RDA: 1.2 mg/day for men; 1.1 for women; 1.4 for pregnant or breastfeeding women

Good food sources: fortified cereals, grains and rice; pork; green peas; lentils

B2 – riboflavin

Riboflavin helps release energy from food, improves absorption of other B vitamins and iron, acts as an antioxidant, and is sometimes used to treat migraines and reduce risk of heart disease and cancer. In food sources, exposure to light quickly diminishes B2 levels, which is why milk is often stored in opaque containers.

RDA: 1.3 mg/day for men; 1.1 for women; 1.4/1.6 for pregnant/breastfeeding women

Good food sources: oats, milk, beef, almonds, eggs

B3 – niacin

In addition to metabolizing nutrients, niacin also helps maintain healthy nerves, skin, heart, digestive system and triglyceride levels. B3’s upper-intake level is 35 mg/day, because too much can cause flushing of the face, arms and chest when ingested in a form called nicotinic acid.

RDA: 16 mg/day for men; 14 for women; 18/17 for pregnant/breastfeeding women

Good food sources: poultry, fish, beef, mushrooms, fortified cereals, peanuts

B5 – pantothenic acid

This vitamin is essential to all life forms, so its presence is widespread in food, making deficiency rare. It metabolizes food, helps make red blood cells and sex and stress-related hormones, processes cholesterol and aids digestion.

Adequate Intake (AI)*: 5 mg/day for men and women; 6/7 for pregnant/breastfeeding women

Good food sources: sunflower seeds, fish, dairy, avocado, sweet potato, poultry, eggs

B6 – pyridoxine

B6 is necessary for brain function, mood regulation, heart and eye health, and protein metabolism, which means you might need more if you eat a lot of protein. Most Americans take in enough B6, but not all of it is bioavailable, which means people (especially vegetarians) are more likely to not get enough B6 than most other B vitamins. Women who take oral contraceptives or people with chronic inflammation may also have low B6 levels.

RDA: 1.3 mg/day for men and women; 1.9/2.0 for pregnant/breastfeeding women

Good food sources: garbanzo beans, fortified cereals, salmon, poultry, potatoes, spinach, bananas

B7 – biotin

Also called vitamin H, biotin helps metabolize carbs, fats and proteins; regulates gene expression; and is thought to strengthen nails and hair. It’s also essential for healthy fetal development. Biotin is better absorbed from plants than from animal sources. Prolonged raw egg-white consumption blocks absorption.

AI: 30 micrograms/day for men and women; 30 (or more)/35 for pregnant/breastfeeding women. The National Institutes of Health recommends up to 300 micrograms daily for everyone.

Good food sources: almonds, sweet potato, eggs, onions, oats, salmon, avocado, dairy, legumes

B9 – folate/folic acid

Folic acid is the synthetic form of B9, found in supplements and fortified foods, while folate occurs naturally in foods. Vitamin B9 is crucial for mental and emotional health. It helps produce DNA, RNA and red blood cells, and enables the body to process iron. B9 isn’t always easy to absorb, so inadequate levels are more common than with most other B vitamins. Low B9 levels during pregnancy can lead to birth defects, so all women of childbearing age should consider B9 supplements. “The key development happens usually before women even know they are pregnant, so they shouldn’t wait until a positive test to start taking folic acid,” Haggans says.

RDA: 400 micrograms/day for men and women; 600/500 for pregnant/breastfeeding women

Good food sources: lentils, peanuts, asparagus, spinach, brussels sprouts, enriched grains

B12 – cobalamin

Beyond metabolizing food, key functions of B12 include keeping nerve cells healthy; producing DNA, RNA and red blood cells; and working with folate to help iron do its job. Up to 15 percent of the population doesn’t get enough B12. More than half of people 50 older have levels below the RDA because they have less stomach acid to digest it, and vegans may struggle to get enough because B12 is naturally found only in animal sources; experts recommend supplements for both populations.

RDA: 2.4 micrograms/day for men and women; 2.6/2.8 for pregnant/breastfeeding women

Good food sources: shellfish, beef, salmon, dairy, turkey, eggs

*Adequate Intake (AI) is based on the minimum that healthy people generally consume; it’s used when not enough information is known to set a recommended daily allowance.

Q: Should I take a B-complex supplement?

Even if you’re low in only one or two of the Bs, some experts recommend taking a supplement that contains all eight B vitamins because they work synergistically, and some evidence suggests that absorption may improve when they’re taken together—or at least when you’re getting enough of each one. They’re water-soluble, so you’re likely to excrete any excess, and their recommended upper limits are either very high or nonexistent (B6 is the main one to watch out for; the upper limit is high but dangerous if you exceed it).

Q: What form of supplement should I take?

B vitamin supplements come in just about any form imaginable. In general, any of the forms are fine. Exception: If you have a digestive issue that makes it hard to absorb nutrients, opt for sublingual (under the tongue), spray or liquid forms, which bypass the digestive system and immediately enter the bloodstream.

Q: Why are numbers missing in the B sequence?

The wacky numbering exists because numbers 4, 8, 10 and 11 got booted from the family when scientists concluded they didn’t meet the essential vitamin qualifiers (necessary for life and not manufactured by the body) after all.