What to Look for in a Multivitamin

Multivitamins are not strictly necessary for all healthy adults who eat a varied, nutrient-dense diet. Dietary guidelines recommend meeting nutrient needs primarily through food when possible. Supplements should complement a healthy diet rather than replace it.

However, research suggests that many people still fall short of key micronutrients, which can make supplementation helpful.¹

A clinical assessment with a healthcare professional may determine whether you are deficient in a particular nutrient. However, multivitamins may also help fill nutritional gaps when the diet is insufficient or if you are at a certain life stage. For example, pregnant women are strongly advised to supplement with methylfolate, while vegetarians/vegans may need to supplement with B12, iron and methylfolate. 

The human body requires a range of vitamins and minerals every day to function optimally. These include:²

• Vitamin A (retinol): Essential for vision, immune defense and normal cell growth and differentiation.
• Vitamin D (cholecalciferol): Regulates calcium and phosphate balance to support bone strength, muscle function and immune signaling.
• Vitamin E (tocopherol): Acts as a lipid-soluble antioxidant that protects cell membranes from oxidative damage.
• Vitamin K (phylloquinone/menaquinone): Required for blood clotting and activation of proteins involved in bone metabolism.

• Vitamin B1 (thiamine): Carbohydrate metabolism and energy production in the nervous system and muscles.
• Vitamin B2 (riboflavin): Energy generation and antioxidant defenses.
• Vitamin B3 (niacin): Forms NAD and NADP, which are essential for energy and metabolism.
• Vitamin B5 (pantothenic acid): Required for synthesis of coenzyme A, supporting energy production and hormone synthesis.
• Vitamin B6 (pyridoxine): Amino acid metabolism, neurotransmitter synthesis and red blood cell formation.
• Vitamin B7 (biotin): Fatty acid synthesis, glucose metabolism and energy regulation.
• Vitamin B9 (folate): DNA synthesis, methylation and normal neural development.
• Vitamin B12 (cobalamin): DNA synthesis, myelin formation and red blood cell production.
• Vitamin C (ascorbic acid): Collagen synthesis, immune function, antioxidant protection and iron absorption.

• Calcium: Bone structure, muscle contraction and nerve signaling.
• Phosphorus: Energy metabolism and structural integrity of bones, teeth and cell membranes.
• Potassium: Intracellular fluid balance, nerve transmission and muscle function.
• Sodium: Fluid balance, nerve impulses and muscle contraction.
• Chloride: Fluid balance, gastric acid production and acid-base regulation.
• Magnesium: Muscle function, energy production and enzyme activation.
• Iron: Oxygen transport and cellular energy metabolism.
• Zinc: Immune function, enzyme activity and DNA synthesis.
• Copper: Redox reactions, iron metabolism,and connective tissue formation.
• Manganese: Metabolic enzyme function, antioxidant defense and bone development.
• Selenium: Antioxidant defences, thyroid hormone metabolism.
• Molybdenum: Cofactor for enzymes involved in sulfur amino acid metabolism and detoxification.
• Iodine: Synthesis of thyroid hormones that regulate metabolism and growth.

Depending on the brand and the formulation, multivitamins can contain a few or many of these vitamins and minerals, but rarely all of them. Nutrients in multivitamins are usually at or below Recommended Dietary Allowances (RDAs) levels, which may be insufficient for correcting a deficiency. The forms of nutrients in multivitamins can also vary widely in terms of their bioavailability (e.g., folic acid vs methylfolate, cyanocobalamin vs methylcobalamin).

Third-party testing means that a supplement has been tested by an independent organization that is not affiliated with the brand. This testing is to verify that the product meets specific quality and safety standards and/or confirms that the claims made on the label regarding ingredients and actions are accurate, as well as screening for unwanted additives or harmful substances. 

Third-party testing is particularly important for ensuring that a multivitamin is safe and effective, as these products are not required to meet Food and Drug Administration (FDA) approval.

Multivitamins are often formulated to support specific health needs required by gender, age and life stages.

• Men
  Men’s multivitamins usually include B vitamins for energy production, zinc for immune and reproductive health and magnesium for muscle function and often contain little or no iron.
  
  
• Women (non-pregnant)
  Women’s formulas usually include B vitamins for energy production, iron to support menstrual losses, along with folate, iodine and calcium to support blood cell development, thyroid function and bone maintenance.
  
  
• Children
  Children’s multivitamins are generally low-dose formulas that may include vitamins A, C, D and B-complex nutrients to support growth, immune function and neurodevelopment.
  
  
• Teens
  Teenage formulas may include calcium, vitamin D and zinc to support rapid growth, bone development and hormonal changes.
  
  
• Pregnancy
  Prenatal multivitamins typically include nutrients to support maternal health and fetal development: folate, iron, iodine, choline, vitamin D and B12 to support fetal development. Vitamin A is usually minimal.
  
  
• Breastfeeding
  Postnatal formulas may provide higher dosages of iodine, B vitamins, vitamin D and choline to support breast milk nutrition and maternal recovery.
  
  
• Older adults
  These formulas should contain nutrients that older adults are typically deficient in, such as folate, B12, vitamin D and calcium for bone health.

Multivitamins are available in a wide range of forms to suit consumer needs and preferences.

• Tablets/capsules: Usually contain a broad spectrum of nutrients.
• Oral sprays: Designed for sublingual delivery and useful for individuals who struggle with swallowing, though typically contain fewer nutrients.
• Gummies: Chewable and ideal for those who struggle to swallow capsules, but typically contain fewer nutrients and are more vulnerable to moisture and heat.
• Liquids/tonics: Easy dosing, ideal for children/older adults. 
• Effervescent tablets: Convenient to use but often contain fewer nutrients and additional excipients.
• Powders: Easy dosing, but requires measuring. 

The bioavailability of nutrients in multivitamins can vary significantly between products. Absorption of specific nutrients depends largely on the form of the nutrient, the digestive function of the individual, the delivery method and interactions with other nutrients/foods.

Vitamins must often be converted into active forms before the body can use them, which requires specific enzymes. Folic acid, for example, is a synthetic form of folate that requires multiple enzymatic steps to become biologically active and inefficiencies in this pathway can limit its usability in some individuals. Methylfolate, on the other hand, is an already active form of folate that can be used directly by the body upon ingestion.

Chelated minerals such as magnesium bisglycinate are better absorbed than oxides and heme iron is absorbed more effectively than non-heme.

The mode of delivery also contributes to bioavailability. Supplements that bypass the digestive tract (such as injectable forms) may be more readily absorbed than some tablets, capsules, gummies or liquids.

Certain fillers and additives can potentially hinder nutrient absorption and may even alter the gut microbiome. Research suggests that some emulsifiers and stabilizers may increase intestinal permeability and inflammation, which can impair absorption.³ Sugars and artificial sweeteners may also affect healthy intestinal microflora.⁴

Antioxidants such as vitamins A, C and E, selenium, zinc and other plant-based phytochemicals all help to neutralize oxidative stress caused by free radicals, which can reduce damage to the body’s cells. They are not necessarily present in all multivitamin formulas, but some clinical studies show that multivitamin supplements containing antioxidant vitamins and phytonutrients can reduce markers of oxidative stress and DNA damage in people with low intake of fruits and vegetables.⁵

If you’re a healthy adult eating a balanced diet, you may not experience dramatic changes after taking a multivitamin. You may notice some improvements in energy, mood and digestive function, but this depends on the product you’re taking and your current circumstances. 

It is normal to experience mild side effects such as slight bloating, gas or softer stools, particularly if the product contains a high amount of vitamin C or magnesium. These effects will pass as your body adapts to the nutrients. 

More serious symptoms such as nausea, vomiting, diarrhea, constipation, headaches or feeling generally unwell can indicate that the product is not suitable for you. Check the ingredients and the forms of the nutrients. It may be too high in iron, vitamin C or an ingredient your body does not need.

Stop taking the product and seek advice from a healthcare professional.