What share of mineral intake comes from food?

A calcium tablet and a bowl of food put the same kind of mineral in by different routes. How much of a day’s total the food carries depends on the mineral, and a Korean adult survey and a U.S. adult survey give different percentages.

What the studies looked at

Woojin Byeon and colleagues, in a 2025 paper, estimated usual intake for 12,314 adults aged 19–69 in the 2019–2021 Korea National Health and Nutrition Examination Survey. Food intake used one 24-hour recall and the National Cancer Institute method, with within- and between-person variance taken from the 2009 survey. A single day of dietary-supplement intake was added on top of that usual food intake. For calcium and iron, the paper reports both the food-only mean and the mean with supplements included.

Xuemin Yan and colleagues, in a 2024 paper, used the U.S. National Health and Nutrition Examination Survey from 1999–2000 through 2017–March 2020, with 48,223 adults aged 20 and older. For each cycle they calculated what percentage of nine minerals came from food and beverages and what percentage came from supplements. Intakes were energy-adjusted to 2,000 kcal by the residual method.

Jill Newman and colleagues, in a 2019 paper, split usual intake for 16,975 people aged 2 and older in the 2009–2012 U.S. survey into three layers: the amount naturally present in food, food after enrichment and fortification, and that total plus supplements. Children are in this sample.

Results

For all Korean adults in the study, mean usual calcium intake was 501.4 mg from food and 564.9 mg from food plus supplements. Dividing 501.4 by 564.9 gives 88.8%. Iron was 10.1 mg and 11.9 mg, which is 84.9%. These percentages divide the group means by each other.

The means split by sex. For men, food was 544.2 mg of 582.8 mg of calcium (93.4%) and 11.4 mg of 12.2 mg of iron (93.4%). For women, food was 456.8 mg of 546.3 mg of calcium (83.6%) and 8.7 mg of 11.5 mg of iron (75.7%). For someone who does not take a supplement, food is the whole of that day’s calcium and iron. The paper notes that more women than men use supplements, and that this is why supplements show up more in women’s totals.

In the last U.S. adult cycle, 2017–March 2020, the paper states these supplement shares: zinc 14.00%, copper 9.22%, calcium 9.04%, iron 7.75%, selenium 6.67%, magnesium 6.07%, potassium 0.51%, and phosphorus 0.40%. Food and beverages are the remainder: zinc 86.00%, copper 90.78%, calcium 90.96%, iron 92.25%, selenium 93.33%, magnesium 93.93%, potassium 99.49%, and phosphorus 99.60%. The supplement share was higher in 1999–2000. Zinc fell from 18.06% to 14.00%.

An earlier slice of U.S. data, ages 2 and older, separates the layers inside iron. Of a mean usual intake of 17.6 mg, 9.1 mg (51.7%) was naturally present in food. Food including enrichment and fortification was 15.0 mg (85.2%). The 5.9 mg difference, 33.5% of the total, was iron added to food. Supplements were 2.6 mg (14.8%). Calcium from food including fortification was 1,026 mg, and 1,122 mg once supplements were added, so 91.4% was food. Potassium was 2,581 mg of 2,590 mg, so 99.7% was food. Zinc was 11.1 mg of 13.7 mg (81.0%). Magnesium was 284 mg of 299 mg (95.0%).

Limits

88.8% and 84.9% divide means for Korean adults aged 19–69. They do not describe one pregnant person, one adult 70 or older, or one person who takes a measured supplement every day. Byeon and colleagues did not model supplements as their own usual intake, and they applied 2009 variance ratios to the 2019–2021 recalls. That Korean paper does not split magnesium, zinc, or potassium into food and supplements.

The U.S. percentages come from other years, other ages, and other calculations. Yan’s figures are energy-adjusted shares from 24-hour recalls. Newman’s figures are ratios of usual-intake means for ages 2 and older. Folding the Korean 88.8% and the U.S. 90.96% into one calcium percentage would match neither survey.

Minerals added to food stay on the food side of these totals. Putting the iron in cereal and enriched grain in the same column as a tablet would drop the 33.5% of mean iron that Newman’s layers assign to enrichment and fortification.

What this means for a log

A meal log keeps the minerals that are in the bowl. On the Korean adult means, that bowl is 88.8% of calcium and 84.9% of iron. On a day with a calcium or iron tablet, the tablet is absent from the photo. On the women’s means, 8.7 mg of 11.5 mg of iron is food, and the other 2.8 mg is that missing column. Fortified bread and cereal stay with the meal.