Nutrient deficiencies are often the culprit behind fatigue, depression, poor mental focus and diminished physical performance. This doesn't mean that taking two multivitamins a day is safe, though. Certain vitamins and minerals may cause toxicity and adverse reactions when consumed in excess.
Taking two multivitamins a day can put your health in danger and cause severe toxicity. When consumed in large doses, certain nutrients may affect the kidneys, increase the risk of bleeding and promote the formation of calcium stones, among other side effects.
Additionally, dietary supplements, including multivitamins, may interact with prescription drugs. Discuss your options with a medical professional. If your diet is balanced, you might not need a daily multivitamin at all.
Are Multivitamins Really Necessary?
More than 75 percent of Americans take dietary supplements, according to the Council for Responsible Nutrition (CRN). About 83 percent of adults aged 18 to 34 and 75 percent of those aged 35 to 54 take multivitamins. These pills are designed to fill nutrient gaps and prevent deficiencies. However, their effectiveness is subject to debate.
As the National Center for Complementary and Integrative Health (NCCIH) points out, a balanced diet should provide all the vitamins and minerals needed for optimum health. The problem is that some people have certain illnesses affecting their ability to absorb nutrients. Others don't get enough nutrients from their diet. If you fall into these categories, a daily multivitamin can help.
Some dietary supplements contain too much of certain vitamins and minerals, which can lead to side effects. Large doses of vitamin A, for example, may cause nausea and vomiting, blurry vision, dizziness and other mild adverse reactions. Over time, you may experience more serious side effects, such as liver damage, joint pain and bone thinning.
Iron supports the formation of red blood cells and protects against anemia. Low levels of this mineral in the bloodstream can affect immune function, cognition and learning abilities. Too much iron, on the other hand, may cause fluid buildup in the lungs, low blood pressure, irregular heartbeat, liver damage, convulsions, fever and coma.
As you see, taking two multivitamins a day can be risky. The side effects will depend on their composition.
Beware that high doses of certain nutrients can worsen your symptoms if you have diabetes, osteoporosis, heart disease or other conditions. Excessive vitamin D, for example, may lead to bone pain, calcium stones and toxicity, according to the Mayo Clinic.
If you have a balanced diet, you probably don't need to take a daily multivitamin. However, there are cases when these supplements can help.
Real Help or Marketing Hype?
Not everyone agrees that multivitamins are beneficial. For example, a December 2013 article published in the Annals of Internal Medicine states that popping vitamin and supplement pills can cause more harm than good.
The scientists reviewed several clinical trials conducted on more than 400,000 participants and concluded that multivitamins have no effect on the risk of cancer, heart disease or early death. On the contrary — certain nutrients, such as vitamin A, vitamin E and beta-carotene may increase the risk of death, especially when consumed in large doses. Researchers have found no association between multivitamins and chronic disease prevention.
Johns Hopkins nutrition experts conducted their own research. After analyzing several studies and reviews, including the one cited above, they concluded that multivitamins don't protect against cardiovascular problems, mental decline, heart attack or premature death. The only exception is folic acid, which may benefit pregnant women.
Other studies have conflicting results. According to a meta-analysis published in the journal Nutrients in August 2018, multivitamins don't reduce blood pressure in individuals with hypertension. They may lower blood pressure in healthy people, but their impact is too small to make a difference.
Furthermore, a large-scale study featured in the June 2016 issue of the Journal of Nutrition found that long-term multivitamin supplementation may reduce the risk of heart disease in men. As the researchers point out, another large study found no association between multivitamin use and heart disease risk, stroke, infarction and cardiovascular mortality in women. Therefore, it's hard to say whether or not these supplements really help.
More Isn't Better
Multivitamins appear to be safe for long-term use. Too much of anything can be harmful, though — and dietary supplements are no exception. Taking two multivitamins a day may cause severe toxicity.
When used in large doses, these supplements can affect every system in your body. Potential side effects include joint, bone and muscle pain, eye irritation, frequent urination, irritability, fatigue, mood swings and changes in bowel habits, as reported by the U.S. National Library of Medicine. You may also experience the following symptoms:
- Unintentional weight loss
- Lack of appetite
- Intestinal bleeding
- Hair loss
- Dry skin
- Cloudy urine
- Bloody diarrhea
Except for niacin, water-soluble vitamins (such as riboflavin and folic acid) are unlikely to cause serious side effects because the excess is eliminated in the urine. Vitamin B3, or niacin, may produce a temporary sensation of heat that lasts up to eight hours, according to the U.S. National Library of Medicine. Other nutrients, though, may have life-threatening side effects when consumed in excess.
Calcium, for example, is essential for teeth and bone health. It also plays a vital role in nerve and muscle function. However, large doses of calcium supplements may lead to kidney stones, constipation and poor absorption of iron and zinc. Additionally, multivitamins containing calcium may interact with antibiotics, thyroid medications, anticonvulsants and other drugs.
As the Mayo Clinic notes, elevated calcium levels in the blood can also affect the kidneys, bones, muscles, heart and brain. This condition, known as hypercalcemia, may cause gastrointestinal symptoms, weaken your bones and depress your mood. Irregular heartbeat, fatigue and excessive thirst are common side effects.
Multivitamin supplements often contain zinc. This mineral supports your natural defenses, contributes to protein synthesis and accelerates wound healing, among other functions. Too much of it can affect copper absorption, reduce good cholesterol levels and affect your immune system. You may also experience nausea and vomiting, abdominal pain, diarrhea and other digestive symptoms.
Another example is vitamin E, a fat-soluble nutrient with antioxidant effects. When used in adequate doses, it keeps your immune system strong, protects against free radical damage, maintains the integrity of cell membranes and fights inflammation. However, it may increase the risk of bleeding when consumed in excess.
When it comes to supplements, more isn't better. Taking two multivitamins a day can affect your health in the long run; these products are not meant to replace a balanced diet. If you're concerned about nutrient deficiencies, make sure your diet is in check before resorting to supplements. Stay on the safe side and consult your doctor in advance.
- CRN USA: "2018 CRN Consumer Survey on Dietary Supplements"
- NCCIH: "Vitamins and Minerals"
- Mayo Clinic: "Vitamin A"
- NCBI: "Review on Iron and Its Importance for Human Health"
- MedlinePlus: "Iron Overdose"
- Mayo Clinic: "What Is Vitamin D Toxicity, and Should I Worry About It Since I Take Supplements?"
- Therapeutic Advances in Gastroenterology: "Nutritional Management of Crohn’s Disease"
- Annals of Internal Medicine: "Enough Is Enough: Stop Wasting Money on Vitamin and Mineral Supplements"
- Hopkins Medicine: "Is There Really Any Benefit to Multivitamins?"
- MDPI: "Effects of Multivitamin and Multimineral Supplementation on Blood Pressure: A Meta-Analysis of 12 Randomized Controlled Trials"
- Journal of Nutrition: "Multivitamin Use and the Risk of Cardiovascular Disease in Men"
- ScienceDirect: "Multivitamin/Mineral Supplements: Rationale and Safety – a Systematic Review"
- MedlinePlus: "Multiple Vitamin Overdose"
- Elderly Health Service: "Vitamins and Health"
- NIH: "Calcium"
- Mayo Clinic: "Hypercalcemia"
- NIH: "Zinc"
- NCBI: "The Role of Vitamin E in Human Health and Some Diseases"
- NIH: "Vitamin E"