Most of us presume that taking a multivitamin every day is a good idea. “Can’t hurt, might help” is what we think. And because many of us struggle with getting in enough vitamin-rich fruits and veggies, surely a little supplement is a reasonable “plan B.” In fact, roughly one-third of American adults take a multi-vitamin.
Well, the answer to whether or not you need a multivitamin is a little bit complicated. First of all, most Americans get sufficient amounts of nutrients from their (albeit sub-optimal) diets that they are not vitamin or mineral deficient in any clinically significant way. Many years ago vitamin and mineral deficiencies (such as vitamin C – which causes scurvy when absent from the diet, vitamin D – which causes soft bones or rickets, iodine – now added to table salt – can cause thyroid disease or goiters) were a serious public health threat. Nowadays, these diseases are rarely seen in the doctor’s office.

That being said, years of research suggest that certain vitamins and minerals are important to supplement under specific circumstances. It would take many book chapters to provide yo
u with all the details and nuances, but I’ll try to summarize the most important points here for you.

• Over 65 years old: As we age, vitamin and mineral deficiencies become more common. Vitamin D, Zinc, and Vitamin B12 are the most common deficiencies in seniors. Vitamin D supplementation is now recommended to improve strength and balance in people over 65. Supplementation has been shown to reduce falls by 19%.
• Age-Related Macular Degeneration: Those with this particular eye health issue may benefit from vitamin supplements rich in lutein, beta-carotene, Vitamins A, C, E, and minerals zinc and copper. Eye health supplements are commonly known under the trade names Ocuvite and PreserVision and may reduce the risk of vision loss as you age.
• Malnutrition: If you are eating limited nutrients (either due to extreme dieting, veganism, or perhaps a medical problem such as stomach ulcers or cancer for example) then there is a greater chance that you have vitamin or mineral deficiencies. Those with poor calorie (or poor food quality) intake should ask their doctor if vitamin or mineral supplementation is needed.
• Wound Healing: Large wounds (from accidents, burns, surgeries or diabetic ulcers, etc.) heal faster if additional vitamin A, C, E and Zinc are supplemented.
• Pregnancy: If you are pregnant or trying to get pregnant, you should definitely supplement a healthy diet with a pre-natal vitamin that includes folic acid, iron, iodine, and calcium.
• Chronic anemia or recent blood loss: If you are anemic due to iron deficiency, iron supplementation is appropriate. Keep in mind that oral iron causes significant constipation.
• Gastric Bypass: If you have had gastric bypass, your absorption of nutrients is likely impaired. Although Vitamin B12 levels are most commonly affected after gastric bypass, folate, zinc, copper, calcium and vitamin D may also be impacted.
• Heavy Alcohol Use: Folic acid and vitamin B1 and B12 may be low and require supplementation in those who drink alcohol heavily and regularly.

Can a multivitamin do harm?
It’s important to know that the Food and Drug Administration (FDA) regulates dietary supplements under a different set of rules than those covering “conventional” foods and drug products. Therefore the contents of multivitamin containers are not independently verified or tested by the US government. It is possible for vitamin companies to sell vitamins and minerals that contain more or less of what is listed on the label.
Quality vitamin and mineral manufacturers voluntarily submit to careful oversight by one of 4 independent companies, and will display their seals (for example US Pharmacopeia, USP, or Consumer Lab) on the bottle.

If your multivitamin causes you to exceed the recommended daily allowance for various vitamins and minerals, you could be at risk for serious side effects. A few examples include:

Calcium – Long term over-supplementation with calcium has been associated with higher rates of heart attacks. The theory is that while calcium is good for the bones, the body may store excess calcium in the walls of heart arteries, causing them to narrow and eventually close.

Vitamin A – High levels of vitamin A can cause symptoms such as nausea and hair loss, and may increase the risk of lung cancer for smokers. There is a risk of birth defects when pregnant women take too much vitamin A.

Iron – In excess, iron can be toxic. Nausea, vomiting, and diarrhea, may progress to seizures, double vision and a rapid heart rate. Iron overdosing is especially dangerous for children.

Manganese – In excess, manganese can cause headaches, muscle cramps, fatigue, and aggressiveness which can then proceed into tremors

Conclusion: Most healthy Americans do not need to take a multivitamin. Specific vitamins and minerals contained in a multi-pill may be helpful when deficiencies are present, but food sources are generally better absorbed. If you have a specific deficiency, supplementing only that vitamin or mineral may be safer than taking a pill that includes more than you need. Look for safety and quality seals of approval from reputable organizations such as Consumer Lab or USP for additional assurance that the vitamin and mineral labels accurately represent their contents.

References
https://ods.od.nih.gov/factsheets/MVMS-HealthProfessional/#en36
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4217039/
https://www.sciencedaily.com/releases/2009/10/091001191659.htm
https://www.ncbi.nlm.nih.gov/pubmed/17209218?dopt=Abstract
https://www.mayoclinic.org/drugs-supplements/iron-supplement-oral-route-parenteral-route/side-effects/drg-20070148

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