Summary
- Babies get their iron with milk, and they turn out okay.
- Limited studies tend to show that milk does not affect iron absorption more than other foods.
- One study using ferric(III) iron showed that milk did not affect absorption.
- Iron absorption studies cannot monitor ferritin, which is a major caveat to their conclusions.
- It seems okay to take milk with iron, especially if you are sensitive to iron on an empty stomach.
Does science really say you shouldn't take iron with dairy?
It’s commonly advised to avoid mixing iron supplements and dairy. The consensus is that dairy inhibits iron absorption due to the presence of calcium and/or casein. However, almost every baby gets their iron along with dairy, and we’ve turned out just fine. In this post, we investigate the science behind whether dairy affects iron absorption.
Why is iron recommended on an empty stomach?
Iron supplements are recommended on an empty stomach to enhance absorption. Without an empty stomach, certain nutrients can bind to the iron, and certain minerals can compete with iron to be absorbed. If these events occur, they reduce how much iron gets to your body.
Without an empty stomach, certain nutrients can bind to the iron, and certain minerals can compete with iron to be absorbed.
How do people study iron absorption in humans?
Typically, iron supplements are (safely) modified to include radioactive iron. The modified iron is administered to subjects under control and experimental conditions. Then, the amount of radioactive iron retained in the subjects’ blood indicates how much of the iron supplement was absorbed.
Do iron absorption studies measure ferritin?
An important shortcoming of the typical methodology is that it only tracks iron in the blood, leaving it blind to iron stored as ferritin. Given that 30% of the body’s iron is stored in ferritin, and ferritin is an important indicator of iron status, this is a major shortcoming.
How does milk affect iron absorption?
There are two questions when considering how milk affects iron absorption: How does milk influence iron compared to water, and how does milk influence iron absorption compared to food? Compared to water, taking iron with milk (or any non-meat food) reduces absorption, typically by a factor of 2-3x. However, adding vitamin C can overcome the effect of milk on iron absorption. Moreover, many people need to take their iron with food to avoid side effects.
adding vitamin C can overcome the effect of milk on iron absorption.
We screened over 200 studies in Google Scholar based on the keyword search {“Iron”, “Milk” OR “Dairy”, Absorption}. Of the 200, we determined nine to be relevant to this analysis. These studies included a clinical trial measuring iron absorption with/without milk. Key results are listed in the table below. Of the relevant studies, 4/9 (44%) found that milk significantly affected iron absorption, while 5/9 (56%) found no statistically significant effect. Based on these reports, we conclude that the evidence does not indicate milk to be worse than other foods at inhibiting iron absorption.
Of the relevant studies, 4/9 (44%) found that milk significantly affected iron absorption, while 5/9 (56%) found no statistically significant effect
Does the type of iron affect how milk influences absorption?
Iron absorption studies are also limited due to comparing different types and doses of iron. For example, in our list of relevant studies, four used iron from food, one used iron from cow/human milk, and the remaining four used four different types of iron supplements. During digestion, the type of iron can influence how food or other nutrients affect iron absorption.
Are there any studies on how milk influences ferric iron(III) absorption?
At Smart Eats, we use ferric iron(III) glycinate. This is very important when considering that milk is primarily thought to inhibit absorption due to the presence of calcium. The theory is that when divalent (+2) calcium and iron are both present in the body, calcium is more preferentially absorbed through a specific ion channel. In this model, trivalent (+3) ferric iron is not subject to the same competition with calcium.
In fact, ferric iron(III) is absorbed through a distinct pathway where receptors bind ferric iron(III), convert it to ferrous iron(II) directly at the cellular, and then push it through a cellular ion channel. Only one study on our list examined ferric iron(III) absorption (using FeCl3), and this study found that milk did not reduce iron absorption when added to the meal.
So, can I take iron with milk?
In conclusion, you can take iron with milk! To maximize absorption, add vitamin C and select a supplement with ferric iron, instead of ferrous iron (you should see "ferric" or "ferrous" iron listed in the ingredients label).
Why does Iron Lift combine iron with milk?
At Smart Eats, we make powder iron supplements, and our non-vegan options deliver the iron with some milk. We do this because milk tastes great, has beneficial nutrients, and makes the ultimate powder more easy to mix. By adding a strong supply of vitamin C and by using ferric iron, our iron powder is designed for high absorption even when delivered with some milk.
List of References and Relevant Details
Listed below are the studies we reviewed. The italicized titles (4/9, 72 subjects) showed a significant effect of milk on iron absorption. The non-italicized titles (5/9, 96 subjects) showed an insignificant effect of milk on iron absorption. For each reference, the study design, number of subjects, and iron source are listed. With over half the studies and participants showing no significant effect of milk on iron absorption, it cannot be concluded that milk inhibits iron absorption.
| Study Title | Year | Journal | Study Design | Subjects | Iron Source |
| Iron absorption from the whole diet: comparison of the effect of two different distributions of daily calcium intake | 1995 | Am J Clin Nutr | 3 meals with labeled iron; consumed with even calcium distribution, or with no calcium midday | 21 | Ferrous Sulphate, 13.3 mg/day |
| Bioavailability in Man of Iron in Human Milk and Cow’s Milk in Relation to Their Calcium Content | 1992 | Pediatri Research | Human milk vs cow’s milk; human milk vs human milk with added calcium | 18 | From milk |
| Milk Inhibits and Ascorbic Acid Favors Ferrous Bis-Glycine Chelate Bioavailability in Humans | 1997 | Nutrient Requirements and Interactions | Iron with/without milk; Iron with/without milk + vitamin C | 14 | Ferrous bis-glycinate/Ferrous ascorbate, 3mg; |
| Effects of different calcium sources on iron absorption in postmenopausal women | 1990 | Am J Clin Nutr | Meal with iron and placebo or calcium | 19 | Ferrous Sulphate, 0.18 mg |
| Effect of calcium intake on nonheme-iron absorption from a complete diet | 1997 | Am J Clin Nutr | High/low calcium diets | 14 | Ferric Chloride, 0.1mg |
| Effects of high compared with low calcium intake on calcium absorption and incorporation of iron by red blood cells in small children | 1999 | Am J Clin Nutr | 5-week high/low calcium diets | 11 | From food, 9 mg/day |
| The Addition of Milk or Yogurt to a Plant-Based Diet Increases Zinc Bioavailability but Does Not Affect Iron Bioavailability in Women | 2005 | Community and International Nutrition | 3 groups: test meal; + milk; + yogurt | 48 | From food, 8.7 mg |
| Calcium from milk or calcium-fortified foods does not inhibit nonheme-iron absorption from a whole diet consumed over a 4-d period | 2004 | Am J Clin Nutr | 4 meals: no calcium + 3 calcium sources | 14 | From food, 13.2 mg/day |
| Effect of milk and fermented milk on iron absorption in ileostomy subjects | 1995 | Am J Clin Nutr | 4 diet periods: 2 soft drinks + 2 milk types | 9 | From food, 12.2 mg/day |
