You’ve heard all about the beneficial vitamins that are used in beauty products, but do you actually know what they do for your body, and the best way to absorb them? Whether it’s through specific foods, supplements, or your new cleanser or eye cream, it’s important to know exactly how each vitamin is helping you. We spoke with New York City-based integrative nutritionist and author Esther Blum (she releases her latest book, The Eat, Drink, and Be Gorgeous Project: 3 Months to a New You, in March 2012), to get the break down on your ABCs.

Vitamin A

What it does for you:

Vitamin A is essential for maintaining the health and repair of your skin, boosting your immune system, and fighting disease. “It helps to clear acne and rosacea, heals lung tissue, and is best absorbed through your diet,” says Esther. Vitamin A is also fantastic for your vision, so when your mom said you should eat more carrots to see better—she was right!

Find it in:

• Cantaloupe
• Carrots
• Cod-liver oil
• Kale
• Sweet potatoes
• Yams

Vitamin B₁
thiamin

What it does for you:

B vitamins are essential for your heart and nervous system, and beans and seeds are an excellent source. “B₁ is crucial for proper cardiac function and nerve conductivity, so you don’t feel jittery and have a healthy heart,” says Esther. “Thousands of people are diagnosed with heart failure each year, but the reality is they actually have a thiamin deficiency.”

Find it in:

• Black beans
• Navy beans
• Peas
• Sunflower seeds
• Tuna

Vitamin B₂
riboflavin

What it does for you:

B₂ protects your cells from oxidative damage—which is what happens when free radicals attack your cells—so it’s essential to maintain the health of your skin. “It also maintains your supply of other B vitamins,” says Esther, who recommends getting your dose by eating a cup of yogurt every day. A way to know you're deficient in B₂ is if you have cracked skin at the corners of your mouth and peeling skin around your nose.

Find it in:

• Calf's liver
• Mushrooms
• Spinach
• Venison
• Yogurt

Vitamin B₃
niacin

What it does for you:

Easily absorbed through food, “B₃ lowers cholesterol, helps your body process fats and converts carbohydrates into energy—making it the ideal nutrient for someone looking to prevent or treat coronary artery disease,” says Esther. It also improves circulation and blood flow, is used to treat acne, and prevents fine lines and wrinkles.

Find it in:

• Asparagus
• Calf's Liver
• Halibut
• Mushrooms
• Salmon
• Tuna
• Turkey
• Venison

Vitamin B₅
pantothenic acid

What it does for you:

B₅ helps to produce healthy fats in your cells, turning them into usable energy which you burn throughout the day. “A great way to absorb the right amount is by eating lots of green leafy vegetables,” says Esther. If you have any fatigue, weakness, or numbness and tingling in your toes, you're probably deficient in B₅.

Find it in:

• Asparagus
• Bell peppers
• Broccoli
• Cauliflower
• Mushrooms

Vitamin B₆

What it does for you:

“B₆ detoxifies homocysteine from the blood— which is an amino acid that is linked to cardiovascular disease,” says Esther. A supplement is the best way to ensure you get the best amount, so take a B-complex with an additional 50mg of B₆ per day.

Find it in:

• Bell peppers
• Shiitake mushrooms
• Spinach
• Summer squash
• Turnip greens

Vitamin B₇
biotin

What it does for you:

B₇ is essential to break down carbohydrates, fats, and protein in the body, which ultimately reduces blood sugar levels and improves cholesterol. “It also promotes healthy skin, hair, and nails by producing skin-moisturizing fats and encouraging cell growth—benefits that all occur by including foods B₇-rich into your diet,” says Esther.

Find it in:

• Avocado
• Broccoli
• Brown rice
• Butter
• Cashews
• Calf's liver
• Eggs
• Meats
• Nuts

Vitamin B₉
folate

What it does for you:

B₉ is responsible for cell division and cell growth. But if you’re pregnant, be careful! “A B₉ deficiency will leave you anemic, and in pregnant women a B9 deficiency can lead to neural tube defects—an opening of the spinal cord or brain which occurs in early human development,” says Esther. This vitamin’s best absorbed via a supplement, so make sure you take 800 micrograms per day for optimal health in addition to the foods below.

Find it in:

• Liver
• Dried herbs
• Sunflower seeds
• Dark leafy greens
• Chick peas
• Asparagus

Vitamin B₁₂

What it does for you:

B₁₂ is a key player in regulating your nervous system, and low amounts can severely affect your mood. “If you’re feeling sad or depressed, test your B₁₂ levels,” says Esther. “It’s best to get your B₁₂ through your diet, but if you’re extremely deficient, your doctor can give you a shot.”

Find it in:

• Cheese
• Eggs
• Milk
• Shellfish

Vitamin C

What it does for you:

Vitamin C is a detoxifier, and one of the most popular—and well known—vitamins. “Humans can’t manufacture C, so you have to absorb it via supplements or through food,” says Esther. “It’s an immune booster, helps to manufacture collagen, and can protect you from cancer!”

Find it in:

• Bell peppers
• Broccoli
• Brussels sprouts
• Citrus like oranges and grapefruit
• Kiwi fruits
• Papaya
• Strawberries

Vitamin D

What it does for you:

“Vitamin D is actually a hormone, which is created when direct sunlight hits your skin,” says Esther. Unfortunately you can’t absorb it while you’re wearing sunscreen, so most dermatologists recommend taking your daily D in a supplement form as well as getting a small dosage from specific foods. “Without it you can feel depressed, gain weight, and develop insomnia,” says Esther.

Find it in:

• Cod-liver oil
• Sardines
• Wild Alaskan salmon

Vitamin E

What it does for you:

Vitamin E is a wonderful source of antioxidants—as all vitamins are—that wards off free radicals. Nuts are a great way to get your fill, and pecans have more antioxidants than any other nut! “E protects us from aging, supports immune function, heart health, colon health, breast health, and alleviates hot flashes during menopause,” says Esther.

Find it in:

• Almonds
• Butter from grass-fed cows
• Eggs
• Meats
• Peanuts
• Pecans
• Poultry
• Vegetable oils
• Walnuts

Vitamin K

What it does for you:

“Kale is one of the best sources of vitamin K, which aids in blood clotting, builds bones, and protects the heart,” says Esther. It can also help diminish dark under-eye circles, and reduces the appearance of redness from rosacea and broken capillaries.

Find it in:

• Beet greens
• Brussels sprouts
• Collards
• Kale
• Spinach
• Turnip