Is There a Benefit to Taking Two One-A-Day Vitamins?

Multivitamin supplements are hugely popular, with more than 50 percent of adults reporting that they take them daily, according to a 2017 Council for Responsible Nutrition survey. As the name implies, the recommended daily dosage for One A Day multivitamin supplements is one per day.

Taking two One A Day vitamins at a time doesn't pose any health risks, but it probably doesn't offer any benefits either.

One A Day vitamins vary in the nutrients and amounts of each nutrient they contain. Certain formulas are created for particular populations; for example, there is a One A Day supplement specifically for women and one specifically for men. There are also formulations for pregnant people and older men and women.

One A Day for women is formulated to improve bone health, physical energy and heart health, while the men's formula addresses heart health, energy and blood pressure. For pregnant people, the formula is aimed at supporting a baby's development and improving bone health for both mom and baby. The One A Day for older adults is formulated to support healthy brain function, eye health and heart health.

​Read more:​ What Is the General Function of Vitamins?

The women's, men's and 50+ One A Day formulas contain all 13 of the essential vitamins, which includes vitamins A, E, D, C, K and the B vitamins:

• B1 (thiamin)
• B2 (riboflavin)
• B3 (niacin)
• B5 (pantothenic acid)
• B7 (biotin)
• B6
• B12 (cyanocobalamin)
• B9 (folic acid or folate)

The pregnancy formula includes all of the above except for vitamin K. This is because the use of vitamin K supplements during gestation may cause jaundice and other problems, as spelled out by the Mayo Clinic.

Depending on the formula, One A Day multivitamins also contain between six and 10 of these essential minerals:

• Calcium
• Iron
• Iodine
• Magnesium
• Zinc
• Selenium
• Copper
• Manganese
• Chromium
• Molybdenum

Each formula varies in the amount of each nutrient it provides, based on the specific needs of women, men, pregnant people and older adults. The amounts are listed on the One A Day labels as a percentage of the daily value, or DV — the amounts established to meet the needs of adults following an average daily diet containing 2,000 calories.

The the One A Day for women contains 100 percent of the daily value for thiamin, riboflavin, niacin, vitamin B6, pantothenic acid, iron, iodine and copper. It also includes:

• Vitamin A: 70 percent
• Vitamin C: 83 percent
• Vitamin D: 125 percent
• Vitamin E: 50 percent
• Vitamin K: 21 percent
• Folate: 167 percent
• Vitamin B12: 250 percent
• Biotin: 3,333 percent
• Calcium: 29 percent
• Zinc: 73 percent
• Selenium: 50 percent
• Manganese: 78 percent
• Chromium 71 percent

The men's One A Day multivitamin provides 100 percent of the DV for vitamin C, riboflavin, folic acid, zinc, copper, manganese and chromium. It also contains:

• Vitamin A: 70 percent
• Vitamin D: 175 percent
• Vitamin E: 75 percent
• Vitamin K: 25 percent
• Thiamin: 90 percent
• Niacin: 90 percent
• Vitamin B6: 150 percent
• Vitamin B12: 300 percent
• Biotin: 25 percent
• Pantothenic acid: 160 percent
• Calcium: 21 percent
• Magnesium: 35 percent
• Selenium: 157 percent

The formula for pregnant people provides 100 percent of the DV for vitamins C, E, D and all of the B vitamins, as well as for the minerals iodine, zinc and copper. It also provides:

• Vitamin A: 50 percent
• Calcium: 15 percent
• Iron: 156 percent
• Magnesium: 11 percent

The formula for men over 50 provides 100 percent of niacin, folic acid and iodine. In addition, it provides:

• Vitamin A: 70 percent
• Vitamin C: 200 percent
• Vitamin D: 175 percent
• Vitamin E: 85 percent
• Vitamin K: 25 percent
• Thiamin: 300 percent
• Riboflavin: 200 percent
• Vitamin B6: 300 percent
• Vitamin B12: 417 percent
• Biotin: 10 percent
• Pantothenic acid: 150 percent
• Calcium: 12 percent
• Magnesium: 28 percent
• Zinc: 160 percent
• Selenium: 167 percent
• Copper: 110 percent
• Manganese: 210 percent
• Chromium: 150 percent
• Molybdenum: 120 percent

The formula for older women is similar to the older men's formula. The differences are:

• Calcium: 30 percent
• Magnesium: 13 percent

You may have noticed that a couple of the formulas contain some nutrients in high amounts:

• 3,333 percent DV for biotin in the women's formula
• 300 percent DV for B12 in the men's formula
• The men's and women's 50+ formulas have 10 times the DV for B12

These sound excessive — but even when doubled, the amounts don't pose a risk. In fact, you could triple or quadruple the dose and not have to worry about any negative health effects.

That's because B vitamins are water-soluble nutrients that can't be stored in the body. Any excess you take in is excreted in urine, and you must replace what you need each day.

If you're still skeptical, consider the Tolerable Upper Intake Limits set by the National Academy of Medicine. The Tolerable Upper Intake Limit, or UL, is the maximum amount of a nutrient the average healthy adult can take without the risk of adverse health effects.

However biotin and B12 don't have a UL, because even large amounts of these vitamins in supplement form haven't been shown to pose a health risk.

Certain other B vitamins do have a UL, including niacin, B6 and folate.

So does that mean you should take two — or three or four — each day? Probably not. It won't hurt you, but it likely won't provide any health benefits. According to Johns Hopkins Medicine, the existing research hasn't shown that taking a multivitamin can reduce your risk of disease.

In conclusion, it's likely a needless expense. It's better to spend your money on fresh, organic fruits and vegetables; whole grains; hormone-free poultry; hormone-free grass-fed beef and dairy; wild-caught fish; and farm-fresh eggs.

These foods are far more effective at providing the nutrition you need than any supplement, and they provide other valuable nutrients, including protein, fiber and healthy fats, as well as antioxidants that have been scientifically proven to fight disease.

​Read more:​ Do Multivitamins Really Work?