How to read a Supplement Facts label, line by line

The front of a supplement bottle is advertising. The back is where the useful information lives. The Supplement Facts panel is a standardized box, and once you know how it's organized, you can size up almost any product in about a minute.

That skill matters more than it might seem. About half of US adults (52%) took at least one dietary supplement in a 30-day period, according to national survey data from 2011 to 2014 (Cowan et al., 2018). Very few of them were ever shown how to read the label. Here's the walk-through, from top to bottom.

First, know who checks what

Supplements aren't regulated like medications. Under US law, the FDA doesn't review the safety of dietary supplements before they go on sale, and no regulatory authority requires a quality review first (Eichner et al., 2019). The company is responsible for what's in the bottle and what the label says.

That makes the label your main source of information. It's also why independent quality seals exist, which is a topic of its own.

Serving size: the line most people skip

Every amount on the panel refers to one serving, and a serving isn't always one capsule. It might be two capsules, three gummies or two scoops. A product that looks generously dosed can turn out to require several pills a day to reach the numbers you see.

• Check the serving size before anything else. "Per 2 capsules" changes how long a bottle lasts and what it really costs.
• Check servings per container. Divide the price by that number to compare products fairly.
• Match the directions to the dose you'll actually take. If the directions suggest a range, work out what you're getting at the low end and the high end.

Amount per serving, and the form in parentheses

Each ingredient is listed with its amount per serving, usually in milligrams (mg) or micrograms (mcg). Probiotics are often listed in colony-forming units (CFU). For vitamins and minerals, you'll often see the source in parentheses, such as "Magnesium (as magnesium citrate) 200 mg." The number refers to the nutrient itself, not the total weight of the compound it comes in.

The form is worth writing down. It's part of what you're paying for, and it's the detail you'll need if you ever want to look up research on that ingredient. Two products with the same number of milligrams aren't automatically the same product.

%Daily Value: a reference point, not a target

The %DV column compares the amount per serving with a Daily Value the FDA sets for labeling. It helps you see at a glance whether a dose is small or large. It isn't a personal recommendation, and more than 100% doesn't automatically mean better.

That last point deserves attention. When government researchers chemically analyzed adult multivitamin/mineral products for a national database, most products already listed amounts at or above the Recommended Dietary Allowances for 12 of 18 nutrients. On top of that, the measured content of nearly every ingredient was higher on average than the label stated, by about 25% for selenium and iodine. Manufacturers often add extra to make up for losses during shelf life (Andrews et al., 2017).

An asterisk or dagger in the %DV column means no Daily Value has been established for that ingredient. You'll see it next to probiotics, herbal extracts and many specialty ingredients.

Below the numbers: blends and other ingredients

Proprietary blends. If you see a named blend with one total weight and a list of ingredients underneath, the company only has to disclose the combined amount. Ingredients in a blend are listed in descending order by weight, but you can't tell whether the fourth one is present at a meaningful dose or a sprinkle.

Other ingredients. Under the panel you'll find "Other ingredients." This is where capsule materials, fillers, flow agents, sweeteners, flavors and colors appear. It's also where you'll spot things that matter for a sensitive gut, such as inulin or chicory root, sugar alcohols or lactose. Here's why inulin in particular can backfire.

The fine print that's easy to miss

• The FDA statement. If a label claims a product supports some structure or function of the body, it has to say the FDA hasn't evaluated that claim.
• Directions and warnings. "Take with food" and "consult your physician if you are pregnant or taking medication" are there for a reason.
• Lot number and best-by date. Handy if there's ever a recall, and a sign the company tracks its batches.
• Company name and contact details. A real way to ask questions, such as whether the product is tested by an outside lab.

A 60-second label check

1. Find the serving size and servings per container.
2. Scan the amounts and %DV for anything far above 100%.
3. Look for proprietary blends that hide individual amounts.
4. Read the other ingredients for anything your gut doesn't tolerate.
5. Check the directions and warnings, and note anything that might matter with your medications.

Then take a photo of the label and bring it to your next appointment. Supplements can interact with medications, which is why the NIH Office of Dietary Supplements encourages people to tell their healthcare providers about everything they take (NIH Office of Dietary Supplements).

Sources

1. Cowan AE, Jun S, Gahche JJ, et al. Dietary supplement use differs by socioeconomic and health-related characteristics among U.S. adults, NHANES 2011-2014. Nutrients. 2018;10(8):1114. PMID 30126136
2. Eichner AK, Coyles J, Fedoruk M, et al. Essential features of third-party certification programs for dietary supplements: a consensus statement. Curr Sports Med Rep. 2019;18(5):178-182. PMID 31082891
3. Andrews KW, Roseland JM, Gusev PA, et al. Analytical ingredient content and variability of adult multivitamin/mineral products: national estimates for the Dietary Supplement Ingredient Database. Am J Clin Nutr. 2017;105(2):526-539. PMID 27974309
4. National Institutes of Health, Office of Dietary Supplements. Dietary supplements: what you need to know. ods.od.nih.gov/factsheets/WYNTK-Consumer/

This article is for general information and isn't medical advice. Talk to your healthcare provider or pharmacist before starting a supplement, especially if you take prescription medication.