How to Enhance Mineral Absorption

How to enhance mineral absorption

Iron is a double-edged sword. If we don’t absorb enough we risk anemia, but if we absorb too much we may be increasing our risk of colorectal cancer, heart disease, infection, neurodegenerative disorders, and inflammatory conditions. See my 3-min. video Risk Associated With Iron Supplements. Other conditions that have been associated with high iron intake include Alzheimer’s, Parkinson’s, arthritis, and diabetes.

Because the human body has no mechanism to rid itself of excess iron, we evolved to tightly regulate the absorption of it. If our iron stores are low our intestines boost the absorption of iron, and if our iron stores are topped off our intestines block the absorption of iron to maintain us at the sweet spot. However, this only works with the primary source of iron in the human diet, the iron found in plant foods. Our digestive system can’t regulate the iron in ingested blood (“heme” iron) as effectively. The iron in animal foods can just zip right through our intestinal barrier, even if we already have too much. We just don’t have as much control. For more on iron, see my videos Iron During Pregnancy and Are Iron Pills Good For You?

Iron overload may be one of the reasons meat consumption has been tied to breast cancer risk. Iron is a pro-oxidant and can induce oxidative stress and DNA damage. Quoting from one of the studies I feature in the video, “A high intake of iron in developed societies may, over time, lead to a physiologic state of iron overload in postmenopausal women, who are no longer losing blood every month. Iron overload favors the production of free radicals, fat oxidation, DNA damage, and may contribute to breast carcinogenesis independently or by potentiating the effects of other carcinogens.”

For more on breast cancer, some good videos to start with include Relieving Yourself of Excess EstrogenFlax and Fecal Flora, and Broccoli Versus Breast Cancer Stem Cells.

Only people with a confirmed diagnosis of iron-deficiency anemia should consider supplementing their iron intake, and even then it can be risky.  Another recent study I explore found a significant increase in oxidative stress within the bodies of women on iron supplements. Therefore, before going on iron supplements I would suggest talking to your physician about first trying to treat it through diet alone. This means eating lots of healthy iron-rich foods like chickpeas and pumpkin seeds while consuming vitamin C-rich foods, such as citrus, tropical fruits, broccoli, and bell peppers. The vitamin C-rich foods improve plant iron absorption, which is why they should be consumed at the same meal. Tea and coffee drinking, on the other hand, should be avoided with your meals since that can impair iron absorption.

For more on nutrient bioavailability, see my videos Take Vitamin D Supplements With MealsCalcium Absorption: Soy Milk Versus Cow MilkRaw Food Nutrient Absorption, and Forgo Fat-Free Dressings?

The whole grain phytonutrient, phytic acid (phytate), partially inhibits mineral absorption, but has a wide range of health-promoting properties such as anti-cancer activity. By concurrently eating mineral absorption enhancers, such as garlic and onions, one can get the best of both worlds by improving the bioavailability of iron and zinc in plant foods. Watch New Mineral Absorption Enhancers Found. Another example of nutrient synergy is the reaction between black pepper and the spice turmeric as described in Garden Variety Anti-Inflammation.

For more on the food-as-a-package-deal concept, see Plant Protein Is PreferablePlant vs. Cow Calcium, and Safest Source of B12.

Michael Greger, M.D.

Image credit: Xbeckie boox/Flickr

  • Funny you should post this as I was just researching how to get iron from plant sources. I had bariatric surgery in the past & my iron levels nose-dived so I’ve been on supplements for a while. It has been about a year and a half since I’ve had my iron levels checked so I do need to get this done but I did stop taking the supplements. Great post :-)

  • Greg Stamper

    Are there solutions for iron overload? My cousin was recently told by her doctor that there is too much iron in her blood and to reduce her intake of dark leafy greens. She is not vegan or vegetarian but I wonder if there are there other plants that she can eat to balance out iron overload?

    • Toxins

      Reducing heme iron would make much more sense to me as the body has no mechanism to block heme iron, which is only from animals. The body can block noneheme, iron, which is from plants. This doctor of yours needs a basic nutrition class!

    • Shaylen Snarski

      Wow… what a horrible doctor to suggest reducing her intake of green leafy greens: one of the healthiest things on the planet that people are not eating enough of! instead of telling her to reduce her red meat and other harmful animal based sources of iron!

  • Dan Hooley

    Dr. Greger: do you know if vegan’s tend to have lower iron stores? I am a vegan and have had my iron stores checked a couple times, and they are on the low end of the spectrum. I am not anemic, and my stores have been pretty consistent for the last couple years. I also eat a lot of iron-rich foods on a regular basis. Are low iron stores something to worry about?

    • Toxins

      Vegans do tend to have lower iron stores and “the requirement for iron is 1.8 times higher for vegetarians.” due to reduced absorption.

      Those that do have lower iron stores absorb iron 20% more efficiently. If you are consuming lots of whole grains and leafy greens you should be ok.

    • Massimo

      Iron deficiency is quite widespread, although not in its most severe forms, but not especially among vegans.
      I’m vegan, my hemoglobin – last test – is 15.9 and I am a blood donor.

  • I wonder if you can comment on this study about sulfur dioxide, used to preserve color of apricots, golden raisins and other dried fruits:

    “Genotoxic effects of sulfur dioxide in human lymphocytes”

    Here is the abstract from Pubmed:

    Sulfur dioxide (SO(2)), which is used as food preservative in apricot
    sulfurization and several fabricated foods, is a common air pollutant.
    The aim of this study was to reveal the possible genotoxic effects of
    SO(2) using in vitro human lymphocytes. The different endpoints of
    genotoxicity: sister chromatid exchange (SCE), micronuclei (MN) tests
    and cell growth kinetics such as mitotic index (MI) and replication
    index (RI) were studied. The cells were treated with 0.1, 0.5 and 1.0
    ppm concentrations of SO(2). It was shown that SO(2) caused significant
    increases in the frequency of SCE and MN in the middle and high dosage
    groups and also induced mitotic delays and decreased MI and RI. In
    conclusion, the results have confirmed that SO(2) has potent
    mutagenicity and it can cause genetic damage leading to a malignancy

  • BPCveg

    Regarding Dr. Greger’s statement: “The iron in animal foods can just zip right through our intestinal barrier, even if we already have too much. We just don’t have as much control.”

    Try looking for evidence for this statement in the sources cited by an earlier  video that made the same claim, namely:

    In the comments section under that video, you can see that several of us vigorously discussed this issue two months ago and found that the articles almost stated the exact opposite of what Dr. Greger claimed. 

    Dissapointingly, Dr. Greger has not responded to the criticisms and is now pushing the same claim once again.

    •  Try this article:

      It indicates a much higher absorption of heme iron than non-heme iron.

      • BPCveg

        Stoaty: Thank you for sending this article, though I believe that your article is still arguing the opposite of what Dr. Greger is claiming.

        Dr. Greger is insinuating that the average meat eater should worry about getting toxic levels of blood iron due to poor control over heme iron absorption. The article you sent doesn’t say that at all. What it says is that iron absorption is a problem for many people with low iron and that heme iron (from meat), has higher absorption than non-heme iron (from plants) and is, thus, beneficial for those people with low iron.

        The only case where iron absorption becomes an issue for meat eaters is the rare genetic condition called heriditary hemochromatosis, where the control mechanisms do not work. I have yet to see any evidence supporting iron overload due to normal dietary consumption of meat in the general population. 

        It is widely accepted in the scientific community that vegetarians and vegans who do not consume heme iron need to take precautions to avoid iron deficiency! That is the real issue and not what Dr. Greger is discussing. I worry that the average person reading Dr. Greger’s page’s will just believe what he says without confirming with original sources.

        • Toxins

          “Humans do not have the ability to remove excess iron and therefore iron
          homeostasis is maintained by regulating the amount of iron entering the
          body from the diet.”

          “In the U.S., a tolerable upper intake level (UL—the Tolerable Upper Intake Level represents the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals in the general population) for total iron intake (from all sources) of 45 mg/day was set for adults…It has been proposed that high iron intakes or high body iron burden may increase the risk of colorectal cancer [95], cardiovascular disease (CVD) [96,97], infection [97], neurodegenerative disorders [98], and inflammatory conditions [99]. The SACN report focused on the link between iron intakes/systemic iron, with colorectal cancer and CVD as these were considered to be the main issues of public health concern in the U.K. The report also considered effects of high exposures to iron on growth in iron replete children. Other conditions that have been associated with high iron intake/systemic iron, e.g., Alzheimer’s disease, Parkinson’s disease, arthritis, and diabetes mellitus, were only briefly considered.”

          This 45 upper limit can be achieved by consuming several sausages, and I would not doubt that people get to this upper limit easily if people are consuming iron supplements in addition to this.

          Approximately 21 to 25 percent of women and 16 percent of men were reported to consume a supplement that contains iron.

          I would agree though that getting too much iron is not an epidemic, but it is a possible concern from some who consume many processed meats and such. I agree that avoiding iron deficiency is a bigger concern in vegans and vegetarians although those consuming well rounded plant based diets do not need to worry about this issue.

          • BPCveg

            Toxins: Please see my detailed response to you below.

        • Kate Scott

          I have personal experience in support of what Dr Greger is saying. I used to eat meat within an otherwise very healthy diet, and have recently learned that I had iron overload for many years all through my meat-eating period (iron levels way, way above the normal range, but I don’t have hemochromatosis). I now have early onset age-related macular degeneration, presumably as a result of this. Since switching to a vegan diet, despite quite a substantial iron intake from plant foods, my iron levels have come down into the normal range

    • Toxins

      The national academies of science agrees with Dr. Greger’s statement: “Heme iron is highly bioavailable and little affected by dietary factors.”

  • donald

    I’ve been pondering the issue of blood letting (donating blood) and it’s possible use to reduce iron load…and also to force the body to make new blood cells as a rejuvinating method.  Any known info on this issue?

    • Toxins

      If one is vegan, I would not be concerned as the body can block nonheme iron, but has  no mechanism to block blood iron from animals.

    • Jo

      A few years ago, I was one point away from needing a blood transfusion due to low iron. It was eight-point something; apparently, doctors recommend transfusions if your iron level falls to seven.

      Had none of the classic signs. No lethargy, not sluggish, was running races during this time. Got my iron up to the lower end in the normal range (twelve-point something), and donated blood — just for the heck of it, to help strangers. My iron fell to nine-point something, checked two weeks later.

      During a regular check-up last week, I was told my white blood cells were small, and that I had anemia — iron levels weren’t tested. Am doubling up on iron again, and I don’t plan on donating blood until I’m in menopause and am not menstruating … just my experience as physically active vegan female (vegetarian since 1994, vegan since 2000).

  • BPCveg

    Toxins: Thanks for engaging in debate on this topic. Let’s take a closer look at your source article: “Iron, Meat and Health” to learn the truth. Article available full text below:

    Pg. 286, paragraph 1: “Body iron content is approximately 4.0 g in men and 3.5 g in women.”

    Pg. 286, paragraph 2: “The body has no means of excreting excess iron. The only way in which iron is lost from the body is from desquamated skin cells and sweat (0.2–0.3 mg/day), urine (<0.1 mg/day), gastrointestinal secretions and hair and, in premenopausal women, from menses."

    My interpretation: When they say there is no means of excreting excess iron, they are referring to active removal of iron from body stores. But, a person with the typical 4.0 grams of iron stores, who stops consuming any iron will lose iron at a rate of about 0.4 mg/day, so it will take about 4000mg/(0.4mg/day) = 10000 days = 27 years to lose it all. As also explained in the article, the main way that iron build up is prevented, is by control over absorption into the body.

    Pg. 294, paragraph 1: "Iron is present in foods as heme or non-heme iron. Heme iron is found almost exclusively in foods of animal origin as hemoglobin and myoglobin. Non-heme iron is found in animal and plant tissues, fortified foods, and supplements. The most important determinant of dietary iron absorption is systemic iron need: more iron is absorbed from the diet in a state of iron deficiency and less is absorbed when iron depots are replete."

    My interpretation: There is, in fact, control over absorption of iron from heme or non-heme origin. It doesn't just build up indefinitely!

    Pg. 299, paragraph 1: "Acute high doses of iron can cause intestinal mucosal damage and systemic toxicity [91]. Lower exposures may interfere with the intestinal uptake, transfer, and systemic use of copper and zinc [92,93]."

    My interpretation: This means that the intestinal absorption mechanisms may stop working properly if someone consumes an extreme amount of iron, whatever the source (plant, animal or supplemental).

    Pg. 299, paragraph 4 (& continued on page 300): "In the U.S., a tolerable upper intake level (UL—the Tolerable Upper Intake Level represents the highest level
    of daily nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals in the general population) for total iron intake (from all sources) of 45 mg/day was set for adults, which was also based on gastrointestinal effects. A UL for iron has not been set in Europe as adverse gastrointestinal effects were not considered a suitable basis to establish a UL for iron from all sources and there were insufficient data regarding other risks."

    My interpretation: Note the words "from all sources" = plant, animal, supplements. Also note the how the upper limit of 45 mg/day can be interpreted. Since every 100 grams of ground beef has 2 mg of iron:
    Therefore, to reach the 45 mg /day US limit from ground beef alone, one would have to consume 100grams x (45 mg/2mg) = 2250 grams = 2.25 kg = 5 pounds of ground beef
    in one day. Therefore, they recommend that people try to eat less than the equivalent of 5 pounds of ground beef worth of iron per day.

    In conclusion, developing iron excess from meat consumption is a non-issue for all practical purposes! People
    who play around will iron supplements can, of course, hurt themselves by exceeding guidelines.

    • Toxins

      I think your making some leaps and bounds with your summary, especially claiming that heme iron will not be absorbed by the body if the body has had enough. This is false as every medical journal points out “Heme iron is highly bioavailable and little affected by dietary factors…Heme is soluble in an alkaline environment and is less affected by intraluminal factors that influence nonheme iron uptake.” The control over iron absorption is primarily with nonheme iron, and this is well established.

      As i stated, one could easily reach the upper limit for heme iron eating PROCESSED meats, such as turkey sausage in this example.

      • BPCveg

        Toxins: If non-heme iron was “less affected” in the sense that you are taking it to mean, then the guidelines would clearly state 45 mg/day applied to heme iron and not to non-heme iron. I read your article carefully and it was clearly indicating that 45 mg/day applied to both forms of iron. In fact, the majority of dietary iron comes from non-heme sources (as stated in your own reference). Therefore, if it were true that non-heme iron could be consumed without limit, then this would be a huge omission in the upper limit guidelines of the USA!

        As you probably know, the upper limit guidelines are always very conservative (i.e. in this case, meant to apply to those who are most sensitive to gastrointenstinal problems). But, let’s look at your sausage example…according to the link you sent, one italian sausage is 56 grams and contains 5.4 mg of iron. So you would have to eat more than 8.3 sausages in one day to exceed the upper limit for iron. By the same logic, though, one cup of cooked lentils contains 6.6 mg of iron. So according to the guidelines, one who consumes more than 6.8 cups of lentils in one day would also exceed guidelines. I personally find both of these cases to be equally ridiculous, so I don’t know why Dr. Greger would even bother to suggest that meat eaters are more at risk of iron overload than vegans.

        • Toxins

          I think you must put it into perspective. The national academy of science does not assume everyone is consuming a vegan diet. You can read in the paper from the national academy of science the method in which nonheme iron is absorbed. Our gut has great control over the absorption of nonheme sources and therefore CAN block excess iron if needed. For the average American consuming an average omnivorous diet, these upper limits must be lumped together as nonheme and heme sources.

          • BPCveg

            Toxins: I have put this all in perspective.

            If you want proof that heme iron will not lead to toxicity in healthy individuals, I suggest that you check out the article titled “Iron absorption from the whole diet in men: how effective is the regulation of iron absorption?”….full text available by the link below:


            Please note that this article is published in the most prestigious journal on nutrition, namely, ‘The American Journal of Clinical Nutrition’ and would thus have undergone a rigorous peer review.

            If you look at the graphs in this article closely, you will see that heme iron absorption is tightly regulated and toxicity will not occur.

            Quoting the authors directly, on page 8 they state:

            “When we directly compared the absorption from nonheme and heme iron, there was a rather steep decrease in heme iron absorption with decreasing nonheme-iron absorption (Figure 5). This means that the control of heme-iron absorption is also very effective. Thus these findings do not support a hypothesis that a high meat intake might lead to an accumulation of iron stores in normal men by bypassing the strong regulation of iron absorption.”

          • Toxins

            The Article you present indeed proves your point quite well and it was the type of evidence I was looking for. So now we can make the assertion that one cannot achieve iron overload. Now I wonder why is it that heme iron has many associations with colon cancers and other cancers as well as certain mechanisms seen with heme iron promoting tumor growth, if we cannot achieve iron overload.

            Studies such as these present the risk:

            Perhaps the issue is not whether we can overload on iron or not, but if we exclusively get iron from heme sources, an issue may arise.

          • BPCveg

            Toxins: I think that you are correct that one of the leading hypotheses for the well-known association between colon cancer and red meat consumption is that heme (which is a pro-oxidant) is causing damage to the intenstinal wall, leading to the cancer. I have the impression that there is not yet a scientific consensus that this is the actual cause of those cases of colon cancer, though, as you point out, there is certainly some evidence to support it.

  • Nick

    Dr. Gregor, I have a question regarding iron absorption. My girlfriend is anemic, and her doctor has recommended her to take iron supplements, which she doesn’t out of conviction. She asked me for some tips on how to boost her iron levels through diet, and this is the recommendations I made to her for now:

    You obviously don’t want to over-do it. Don’t make it a life purpose of eating a crazy amount of food rich in iron for now, but instead, make it a purpose to absorb better the iron you ingest. If this fixes the issue, good. If not, we can explore foods rich in iron. Also, don’t change your habits (as in: keep drinking coffee in the morning and tea as well). Ergo:

    1) Have a glass of orange juice in the morning

    2) Add red onions in your salad

    3) Add lemon juice (1/2 of a lemon is more than enough) in your tea

    4) Add garlic and onions in most of your meal, especially when eating pasta (due to Pectin)

    5) Eat a kiwi, orange or any other fruit rich in vitamin C after a meal

    Thank you!

    P.S. I was at your conference in Montreal this Sunday, loved it!

  • Arun Mukherjee

    Am worried about my recently diagnosed low hemoglobin. I eat lots of beans and lentils as well as greens. And do eat onions and garlic and broccoli and peppers in my meals. I would hate to have my doctor point a finger at my plant-based diet. Would love suggestions.

    • Low Hemo Vegan

      Arun – Hope you receive an answer. Was just diagnosed low hemoglobin also but am thinking am missing the C so just increased my rosehip intake with meals and will be more vigilant with other sources but don’t do citrus well. Am not sure what I’m missing but do not intend to go on Feosol as advised. Since this is an old video we probably won’t get the answer here.

      • Arun Mukherjee

        Thanks for sharing. I do mix citrus with my greens etc. Dr. now wants to test for internal bleeding. Let us see what transpires.

  • Gregory Chiasson

    Lately this has been on my mind quite a bit. more often than not, plant foods that are high in iron are also high in calcium, such as chia seeds, blackstrap molasses and sesame seeds. from what i’ve read, calcium seems to inhibit iron absorption, so does the high calcium content of foods such as chia seeds block the iron from being absorbed? or would one simply have to eat something high in vitamin C to negate the calcium’s effect?

    • Joseph Gonzales R.D.

      Yes. It could for foods that are super high in calcium and low in iron. This is why toddlers drinking too much milk (high in calcium) can have higher risk of iron-deficient anemia. Although foods like chia have both iron and calcium I don’t think it has the same concern as seen milk. Those minerals may compete for absorption, but with high amounts of both iron and calcium I suppose the body (being a very efficient biochemist) knows how to control for proper absorption. If concerned about mineral levels I suggest asking your doctor about the right testing. Hope that is semi-helpful.

  • Do onions and garlic enhance absorption of other minerals such as calcium, or only iron and zinc?

    • Joseph Gonzales R.D.

      From what I see only iron and zinc.

  • Youcef

    Dr Greger: Any guess on how the same action that improves iron and zinc absorption may also affect the absorption of magnesium and calcium? Could it inhibit the action of phytates in the traditional understanding of phytates as chelators? Or the contrary and prevent make iron and zinc more available at the cost of making magnesium or calcium less available?

    • Joseph Gonzales R.D.

      Complex question, Youcef! I am not entirely sure. I don’t think vitamin C helps the absorption of calcium and magnesium like it has been shown to do with iron. My understanding is that phytates will only affect those with nutritional deficiencies (think third world countries). For the majority of folks phytates in foods can be extremely healthful, as Dr. Greger explains. It seems garlic and onions enhance absorption. Some research shows consuming too much calcium may lower Vitamin D levels. I think all micronutrients work together and as you mentioned tend to compete with each other for absorption. I found some info on magnesium from NIH. My view is a well-rounded diet rich in whole-plant foods can provide all the nutrients needed without worrying about mineral absorption, unless of course your doctor has concerns or some levels appear low.

      • Youcef

        Well, I used to share the same belief as you @disqus_wnYOIlS4ks:disqus until I started being interested in soil science and independently, nutrient variations in the same foods. I’ve only covered Selenium and Iodine so far, but it appears very clearly that at least trace elements vary a lot in foods.
        Selenium :
        Catechins in tea (only as further evidence of concept):
        Iodine: yet to be published.

        Based on variations in soils, and additionally variations in uptakes and plant synthesis, I was forced to reconsider my assumptions that a “well-rounded diet rich in whole-plant foods, unless of course your doctor has concerns or some levels appear low.” I may agree with you if doctors tested all the minerals but they don’t. The minerals looked at only a few minerals, analysis is only blood-based (which doesn’t always represent reserves) and even then often indirect metrics…I could go on :) I’d be glad if basic nutrient tests were done with a pinch of blood (or other) and did either direct or highly reliable indirect measurements.

        • Joseph Gonzales R.D.

          Thanks for sharing your thoughts! I like your site, and wow, I see some of Dr. Greger’s information how neat! I am interested in healthful soil and nutrient availability. Please help keep us informed here and continue to post.

  • Jennifer

    Question, I have iron deficient anemia, even from when I ate meat. I am now primarily vegetartian and my doctor now says my iron levels are too low, that I cannot get enough iron just from food and that I need to go on supplements. However, after several months of taking the supplements there was not a noticeable improvement in iron levels in my blood tests. Should I assume I have a mal-absorption issue? Would I need to get iron shots? Or are there in fact combinations of foods that will allow me to absorb iron?

  • Shaylen Snarski

    There is 100% DV of iron in my multi, is this safe?

    • Kevin

      I could see maybe 15% or something to help fill in the gaps, but 100% seems completely unnecessary.

  • Levon

    I recently heard that soymilk and even breast milk inhibits iron absorption. Is there any data to back that up. My wife is still breastfeeding and we want to make sure our 7 months old gets enough iron from the rest of the food we give him.

    • Shaylen Snarski

      I never heard that, but I think what the case may be is that a lot of plant milks you buy in stores are fortified with calcium and calcium competes with iron so it can block some iron absorption. I read that dairy blocks iron absorption for this reason, though I think people who eat dairy eat a lot more of it (with virtually every meal) than someone drinks plant milk throughout the day. I would just make sure to not drink it with every meal or make your own, unfortified plant milk. Almond milk is surprisingly easy to make.