This question is about Nutrition
While not everyone needs a multivitamin, it may prove beneficial for some groups and individuals, by providing functional benefits and filling nutrient gaps [ 1 2
A poor diet usually consists of refined sugars, processed foods, and trans-fats, and has been linked to a risk of chronic disease, obesity, inflammation, and cancer, as well as a risk for nutritional deficiency [ 1 3 4
As such, multivitamins and dietary supplements should be consumed in tandem with a nutritious diet, not in place of it. Supplements are intended to supplement dietary intake, not replace it.
Furthermore, some people have higher needs for specific nutrients (such as in hypermetabolic states, heavy training, pregnancy and/or lactation), or malabsorption issues. For these reasons, taking a safe, well-researched multivitamin can be beneficial, as it can fill in the gaps and make up for shortfalls in your diet [ 2
Fulgoni, V. L., 3rd, Keast, D. R., Bailey, R. L., & Dwyer, J. (2011). Foods, fortificants, and supplements: Where do Americans get their nutrients?. The Journal of nutrition, 141(10), 1847–1854. https://doi.org/10.3945/jn.111.142257
Rautiainen, S., Manson, J. E., Lichtenstein, A. H., & Sesso, H. D. (2016). Dietary supplements and disease prevention - a global overview. Nature reviews. Endocrinology, 12(7), 407–420. https://doi.org/10.1038/nrendo.2016.54
Schulze, M. B., Martínez-González, M. A., Fung, T. T., Lichtenstein, A. H., & Forouhi, N. G. (2018). Food based dietary patterns and chronic disease prevention. BMJ. https://doi.org/10.1136/bmj.k2396
Fadnes, L. T., Økland, J.-M., Haaland, Ø. A., & Johansson, K. A. (2022). Estimating impact of food choices on life expectancy: A modeling study. PLOS Medicine, 19(2). https://doi.org/10.1371/journal.pmed.1003889