What you should know about multivitamins

Whether a multivitamin is ‘good’ or not depends on its formulation, ingredients, potency, quality assurance, manufacturing, and many other factors. There are thousands of multivitamin products available on the market now, and all vary significantly in terms of quality and efficacy.

A multivitamin has no specific set of ingredients, but the term ‘multivitamin’ generally refers to any supplement containing three or more vitamins or minerals, sometimes with added herbs, hormones, or enzymes, each at a dose less than the tolerable upper intake level (as set by the US Food and Nutrition Board)¹.

Most products on the market include a combination of essential vitamins and minerals, designed to fill nutritional gaps in the diet and/or support specific health conditions.

Key components of most multivitamins are: 

• Vitamins: Water-soluble (B-complex, C) and fat-soluble (A, D, E, K).
• Minerals: Iron, magnesium, calcium, zinc, iodine, selenium, and other trace minerals. 
• May also include amino acids, herbal extracts (e.g, ginger, garlic, ginkgo), enzymes, probiotics, antioxidants, and other nutrients to support overall health, metabolism, and bodily functions.

If you are deficient in one or more nutrients, a multivitamin may not be enough to support your health. Multivitamins generally only provide small amounts of many nutrients rather than a dose high enough to reverse deficiency. Some deficiencies (e.g. iron, B12, folate) may require therapeutic dosing.

Although multivitamins are not meant to replace a healthy diet, supplements can help to reduce inadequacies in micronutrient intake when the diet is not sufficient. In the US, common dietary deficiencies include vitamins A, C, D, and E and calcium, magnesium, iodine, and iron².

Multivitamins can support individuals who are at risk of nutrient deficiencies due to health conditions, genetic mutations, or dietary choices. 

B vitamins play essential roles in converting the food we eat into energy. Supplementation with active B vitamins can help to improve energy levels in conjunction with a healthy diet.

Taking a multi-vitamin supplement may improve immune function, primarily in individuals with existing deficiencies or older adults (55 and older)³.

All multivitamins work in different ways. Signs that your multivitamin is working may include improved energy, fewer infections, improved mood, clearer thinking, healthy skin and nails, and other improvements to your mental and physical health. However, individual responses to multivitamin supplementation will vary.

Yes, it is generally recommended to take your multivitamin every day, as daily supplementation can help to maintain levels of specific vitamins and minerals or restore low levels so that your body has what it needs to function properly. 

Some people prefer to take their multivitamin in the morning as B vitamins support energy production, metabolism, and mood.

Although a nutritious diet should reduce your need for supplementing with a multivitamin, some people may not be able to obtain all the nutrients they need from diet alone. This may be due to digestive impairments, genetic variants (such as MTHFR), age, medications, or certain health conditions. Life stages such as pregnancy also increase the body’s demand for certain nutrients, such as iron and folate, which food cannot provide at the doses needed.

Like all supplements, multivitamins expire. Every product is different, so check the expiry date before purchasing. It is generally not recommended to take an expired product.

Multivitamin deficiency symptoms
You cannot be deficient in a multivitamin itself, as a multivitamin is a supplement and not a nutrient. However, taking a multivitamin can help prevent or restore deficiencies in the vitamins and minerals it provides. Symptoms occur when the body lacks specific nutrients, not the multivitamin as a whole.

Deficiency in each of the 13 vitamins can produce distinct physical and mental symptoms.  While specifics depend on the vitamin, these deficiencies affect cellular metabolism, neurologic function, blood cell formation, and tissue integrity⁴.

Megaloblastic anemia and related symptoms (fatigue, weakness) are common symptoms of vitamin B12 deficiency due to impaired DNA synthesis in blood cells. Low B12 can also lead to numbness/tingling in the limbs and muscle weakness.

Fatigue, malaise, muscle and joint pain, anemia, bruising, bleeding gums, poor wound healing, frequent infections.

Night blindness and other vision problems.

Muscle weakness, generalized fatigue, frequent infections, low mood.

Multivitamins should not cause side effects when taken in the correct dosage. However, excess intake of certain nutrients can cause adverse effects, such as gastrointestinal upset. For example, high doses of calcium or iron can cause nausea and/or constipation.

Water-soluble vitamins are unlikely to cause toxicity, as anything the body cannot use immediately is flushed out of the body. However, excess B6 can result in photosensitivity and neurotoxicity.

Fat-soluble vitamins are more likely to cause toxicity as they are stored in the body. High doses of Vitamin E can result in bleeding associated with antiplatelet action as well as diarrhea, weakness, blurred vision,. Vitamin A toxicity may increase the risk of birth defects and cancer when taken in excess⁵.

Some multivitamins contain minerals that can bind to certain types of antibiotics. Specifically, chelation can occur between fluoroquinolones and the minerals iron, calcium, zinc, and magnesium, which leads to a formation of an insoluble complex compound that is poorly absorbed from the gastrointestinal tract⁶. Taking these minerals at the same time as an antibiotic can significantly decrease the efficacy of the antibiotic.

Talk to your healthcare professional about taking a multivitamin with antibiotics.