The ABCs of Vitamins: Benefits of Vitamins A, C, D, E, K, and B

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Dr. Mehmet Oz, M.D. Posted on February 13, 2024

Half of American adults—including 70% of folks over 70—take a vitamin regularly. According to Harvard's T.H. Chan School of Public Health, a third of those use a comprehensive multivitamin.^[1] Vitamin D is the most frequently taken single vitamin supplement.^[2]

But whether you're an enthusiast or don't use vitamin supplements, chances are you need to learn a lot about which foods deliver which vitamins, what each one does in your body, or the right amounts and combinations of supplements to take.

Do You Need A Multivitamin or Other Supplements?

The US Centers for Disease Control and Prevention says^[3] that women of child-bearing age should take 400mcg of folate daily—in addition to eating a diet rich in broccoli, brussels sprouts, leafy greens, chickpeas, and kidney beans—to help prevent neural tube defects and spina bifida in their offspring.

It can be challenging for many people to get enough vitamin D through exposure to the sun and foods with vitamin D—especially in the winter—so a supplement may be helpful. Also, vegans and some vegetarians may have difficulty ingesting enough vitamins to maintain a healthy metabolism, bones, and immune systems, form red blood cells, and maintain the central and peripheral nervous systems^[4].

A 2022 study in the journal Nutrients^[5] says that intake and levels of vitamin B12 (along with iron, zinc, iodine, calcium, and bone turnover markers) are generally lower in plant-based dietary patterns than in meat-eaters. Vegans had the lowest vitamin B12 (calcium and iodine) intake and lower bone mineral density. Meat-eaters were more likely to be deficient in vitamins E and folate.

As for the other vitamins, it is of primary importance that you get them through a healthy, well-balanced, plant-centered diet that includes (if you want) lean poultry and fatty fish like salmon. Your dietary goal is to enjoy an anti-inflammatory, minimally-processed diet that delivers up to nine servings of fruits and vegetables daily, healthy fats (extra virgin olive oil), and 100% whole grains.

The big picture: But… there is always a but…according to the National Health and Nutrition Examination Surveys ^[6], 95% of folks in this country don't get the daily requirement for vitamin D, 84% for vitamin E, 45% for vitamin A, and 46% for vitamin C. Many people need to up their intake to make sure they don't have to contend with the health risks that come from vitamin deficiencies.

ABCs of Vitamins: A, C, D, E, K, and all the Bs

Research has provided many insights into the importance of these nutrients.

Vitamins A, D, E, and K are fat-soluble and are stored in your body's liver, fatty tissue, and muscles.
Vitamin C and the Bs are water-soluble. You must ingest them continually to avoid shortages and deficiencies (they pass out of your body through your urine).
An exception: B12 can be stored in the liver^[8].

Vitamin A Benefits + Food Sources

Vitamin A^[9] helps you maintain healthy teeth, bones, soft tissue, mucous membranes, and skin. The RDA is 900mcg for males and 700mcg for females. It is found in healthful foods such as salmon, herring, and sardines.

You can also boost your vitamin A levels by taking beta-carotene ^[10]. In the body, it is converted into vitamin A and offers the vitamin's benefits, plus it helps control inflammation (as an antioxidant) and protects your vision. Orange foods like carrots, butternut squash, and sweet potatoes are good sources.

Since excess vitamin A can have adverse side effects, getting your "A" from beta carotene is smart: Your body only converts it into vitamin A if you need it^[11]. There is no RDA for beta carotene. Interested in learning more? Check out "Have You Heard of Beta Carotene? Here Are the Top 5 Benefits."

Vitamin B Types + Benefits

B vitamins contain what are called methyl groups—which are chemicals that play a role in a wide range of bodily functions, including converting fats, proteins, and carbs into energy and helping build DNA and RNA. But those methyl groups can only do their jobs when the vitamins go through a process in your body called methylation. Some folks have bodily systems that are good at that—but some (around 30%)^[12] cannot because of a genetic mutation. So, for them, taking already methylated vitamins helps ensure they get the beneficial nutrients they need. However, a nutritious diet and healthy lifestyle that supplies and preserves B vitamins are basic requirements for optimizing your health. Then, adding additional nutrition boosters can offer benefits.

8 Types of Vitamin B

Thiamin (vitamin B1) helps turn calories into energy and maintains the health of your skin, hair, muscles, brain, and nerve function. It's found in brown rice, soy milk, watermelons, and acorn squash.^[13] The recommended daily amount is 1.2 mg for males and 1.1 mg for females.
Riboflavin (B2) also helps convert food into energy and helps maintain the health of your skin, hair, blood, and brain. It's in milk, green leafy vegetables, meats, whole and enriched grains and cereals. The recommended daily amount is 1.3mg for males and 1.1mg for females.
Niacin (B3, nicotinic acid), in addition to converting food into energy, helps keep skin, blood cells, brain, and nervous system healthy. You can find it in meat, poultry, fish, fortified and whole grains, mushrooms, potatoes, and peanut butter. The recommended daily amount is 16mg males, 14mg females.
Pantothenic acid (B5) fuels your energy and helps make fats, neurotransmitters, steroid hormones, and hemoglobin. It shows up in chicken, whole grains, broccoli, mushrooms, avocados, and tomato products. The recommended amount is 5mg a day for males and females.
Pyridoxine (B6) has a wide range of benefits: It helps convert tryptophan to niacin and the neurotransmitter/hormone that's important in regulating sleep, appetite, and moods. It also helps make red blood cells and affects immune function and cognition. You can get the recommended daily amount of 1.3mg for males and females 31 to 50 and 1.7mg for males and 1.5mg for females 51+ from fish, poultry, legumes, soy products, potatoes, bananas, and other non-citrus fruits.
Biotin (B7)^[14] helps enzymes break down fats, carbohydrates, and proteins in food and also helps regulate gene activity. It shows up in whole grains, soybeans, and fish. The recommended daily amount is 30mcg for males and females. Fun fact: The name biotin comes from the Greek for life or sustenance since the nutrient is vital^[15] for healthy fetal development and for the health of your skin, hair, eyes, liver, and nervous system^[16].
Folate (B9) not only helps protect a fetus from neural tube defects but also is important for new cell creation. Fun fact: B9 is called folate because it is found in foliage, like spinach and other leafy greens^[17]. It is also found in fortified grains, cereals, asparagus, okra, spinach, turnip greens, broccoli, legumes, and orange and tomato juice. The recommended amount is 400mcg a day for males and females. However, your body has to be able to convert folic acid into folate for you to reap its full benefit—and some folks (estimated at 30%^[18]) cannot do that because they have a genetic mutation that prevents it^[19]. But if you take methylated folic acid, AKA methyl folate, you'll get the benefits you seek.
Cobalamin (B12) is important for making new cells and breaking down some fatty acids and amino acids (the building blocks of proteins). It also helps make red blood cells and DNA and protects nerve cells. It's found in poultry, fish, fortified cereals, and soy milk. The recommended amount is 2.4 mcg a day for males and females. An optimal formulation for a supplement is methylcobalamin. For more info, check out "Everything You Need to Know About Vitamin B12 (Cobalamin)."

Vitamin C Benefits + Foods

Vitamin C is used by the body to make collagen, neutralize unstable cell-damaging molecules, strengthen the immune system, and make the neurotransmitters serotonin and norepinephrine.^[20]Citrus fruits, berries, broccoli, bell peppers, spinach, strawberries, tomatoes, and brussels sprouts can help you meet the recommended daily intake of 90mg for males and 75mg for females; smokers should add 35mg. For more information, go to "What Does Vitamin C Do? Immune Health, Skin Benefits, and More."

Vitamin D Benefits + Recommendations

Vitamin D is important for maintaining healthy blood levels of phosphorus and calcium—helping to strengthen bones and teeth. Preliminary research indicates it may have a role in immune function, too. Fatty fish like salmon are a great source. The recommended intake is 600IUs for folks aged 31 to 70: 15 mcg and 800IU for those 71 and older. I recommend D3. For details on the science-backed benefits of this vitamin, check out "Vitamin D: 6 Researched Benefits."

Vitamin E Benefits + Foods

Vitamin E is important in protecting cells from damage from unstable molecules, and it also protects vitamin A from damage. It appears in vegetable oils, wheat germ, sunflower seeds, leafy green vegetables, trout, and nuts/peanuts^[21]. The recommended daily intake is 15mg. For an explanation of the different forms and the wide-ranging benefits, check out "The Different Forms and Benefits of Vitamin E."

Vitamin K Benefits + Forms

Vitamin K comes in two forms—K1 and K2. You can get a good dose of K1 from leafy greens like spinach, broccoli, canola, and soy oils. The most healthful sources for K2 are sauerkraut, natto and miso. Although your body can convert K1 to K2—it's inefficient. The NIH Office of Dietary Supplements says your body only absorbs 4% to 17% K1 from spinach as from a tablet. Taking a K2 supplement with vitamin D can help boost your intake, but be careful. Vitamin K can affect blood clotting and shouldn't be taken with blood thinners. The Academies of Medicine's Food and Nutrition Board^[^22] says, "No adverse effects associated with vitamin K consumption from food or supplements have been reported..." Foods that contain some K1 and K2 include eggs, milk, spinach, broccoli, sprouts, kale, and collards. There is no recommended daily allowance or intake. To learn more, read "Vitamin K Health Benefits, Deficiency, Food Sources and More."

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