“A multivitamin is sort of like an insurance policy,” says Singh. As he explains it, in an ideal world, we’d be able to get the minimum required nutrients from our diets in the form of food. But as we know, this isn’t always possible. For the times when we miss some nutrients (eg, we go on a trip, we scarf down a granola bar for lunch, or we just don’t have the effort to cook those leafy greens after work), a multivitamin can help fill in any gaps.
The goal of this is to make sure you’re not developing a deficiency in any one nutrient, which is increasingly common. According to the CDC’s Second Nutrition Report1, just under 10 percent of the US population had a nutritional deficiency. This depends on a lot of factors like age, gender, and ethnicity, and that number could be as high as 30 percent in certain populations. The report showed the most common deficiencies are vitamin B6, iron, and vitamin D—all of which are typically found in a multivitamin.
If you’re ready to click “purchase” on a multivitamin, there’s one thing to know first: they’re not all created equal. “I try to find a multivitamin from a high-quality company with a good reputation,” says Singh. According to him, some green flags are using organic ingredients, natural flavorings and colorings, and products that are free from fillers, dyes, and gluten.
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Once you’ve found a high-quality product, you might wonder how long it takes before you know it’s working.
There aren’t any hard-and-fast rules, but experts recommend waiting anywhere from a few weeks to a few months before expecting a change. And even then, according to Singh, you’re unlikely to notice anything too drastic (but that doesn’t mean your supplement isn’t doing its job).
That’s because multivitamins are meant to supply a little bit of a lot of different nutrients to maintain healthy levels versus actually correcting a deficiency. If you have a true deficiency, a multivitamin probably doesn’t contain enough of that nutrient to correct it.
For example, if you have a vitamin D deficiency, doctors recommend taking at least 5,000 IUs of vitamin D a day to correct a deficiency versus just maintaining healthy levels. Why? Because according to certified clinical nutritionist Lindsay Boyers, it takes 1,000 IU of vitamin D3 per day to increase your levels2 by about 10 ng/ml4, but the typical multivitamin only contains about 400 IUs of vitamin D.
That said, there are some hints that your multivitamin is working: