Ferrous Sulfate: Benefits, Side Effects, Best Time to Take It & More

Ferrous Sulfate

(Iron Sulfate)

Evidence: Very High
Potential Benefits: Reasonable
Safety: Low

What is ferrous sulfate?

Ferrous sulfate is a popular type of supplemental iron. While iron is an essential mineral necessary for many functions in the body, iron supplements like ferrous sulfate are only helpful if you are deficient in this mineral. If you already get enough from food, taking additional iron through supplements is discouraged as too much iron can be just as problematic as too little. This article is about the main benefits of ferrous sulfate, its potential side effects, the best time to take it, and more.

What does ferrous sulfate do?

The main and only reason to take ferrous sulfate is to raise iron levels in the body.

The main function of this mineral is carrying oxygen from the blood into the tissues. Losing this ability results in anemia, which leads to most problems related to iron deficiency. This nutrient is also necessary to utilize oxygen to burn food for energy. Iron is also needed to make the thyroid hormone so getting an insufficient amount could lead to hypothyroidism. It can defend against oxidative stress but also cause oxidation if you have too much iron in your system.

While getting enough iron is vital for optimal health, getting too much is just as common and can be just as harmful as too little. Iron overload often leads to symptoms similar to a deficiency, such as dizziness, fatigue, depression, and hair falling out. On top of this, too much iron can cause high cholesterol, diabetes, pain in the joints, chest, or abdomen, and faster aging. It also contributes to Alzheimer’s and Parkinson’s disease. While a deficiency causes pale skin, getting too much iron makes your skin more colored (typically more brown, bronze, or gray). This is the most notable difference between deficiency and overload. If you were to experience these symptoms but kept consuming high amounts of iron, it would eventually cause hemochromatosis. This condition can cause serious liver damage and heart problems.

Potential benefits

It is important to note that all of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.

Many possible benefits fall under the umbrella of ‘correcting a deficiency’ and are therefore not mentioned in the article. If you are deficient in iron, ferrous sulfate supplements can affect your cognition, performance, and overall health in a remarkably positive way.

Benefits

Correcting or preventing a deficiency – Iron deficiency can be terrible for your health and overall quality of life. Fortunately, a severe deficit is relatively rare. A mild deficiency is much more common and can lead to many problems mentioned later in the article. If you are experiencing symptoms of deficiency or know that your iron levels are too low, correcting a deficiency is the main and only benefit of ferrous sulfate supplements.

Possible side effects

These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to high doses.

Constipation – This side effect applies mainly to the ferrous sulfate and ferrous fumarate forms of iron and rarely occurs if you take other forms.
Nausea – Nausea caused by ferrous sulfate supplements is not dangerous but can be unpleasant.
Bacterial overgrowth – Just like constipation, this effect mainly applies to ferrous sulfate and ferrous fumarate.
Headaches – Interestingly, those who take ferrous sulfate every other day are more likely to experience headaches than those who take this mineral.
Iron toxicity – While getting enough iron is vital for optimal health, getting too much is just as common and can be just as harmful as too little. Iron overload often leads to symptoms similar to a deficiency, such as dizziness, fatigue, depression, and hair falling out. On top of this, too much iron can cause high cholesterol, diabetes, pain in the joints, chest, or abdomen, and faster aging. It also contributes to Alzheimer’s and Parkinson’s disease. While a deficiency causes pale skin, getting too much iron makes your skin more colored (typically more brown, bronze, or gray). This is the most notable difference between deficiency and overload. If you were to experience these symptoms but kept consuming high amounts of iron, it would eventually cause hemochromatosis. This condition can cause serious liver damage and heart problems. The best way to prevent toxicity (besides not consuming excessive amounts of this mineral through diet and supplements) is by donating blood. Bleeding and donating blood can quickly and reliably rid you of excess iron.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.

Who should not take ferrous sulfate?

You should probably avoid taking the supplement if you:

have a specific HFE gene mutation (Genetics are the main reason why people experience severe hemochromatosis. The HFE gene regulates how well you absorb iron. About 25% of the population has one of the HFE gene mutations that increase the risk for hemochromatosis. Because of this gene, hemochromatosis mainly affects white people and rarely happens to those born in Asia and Africa.)
consume enough iron from food
experience a severe adverse reaction after taking the nutrient
eat high amounts of meat
are willing to take a different form of iron
experience symptoms of iron overload and hemochromatosis

Who will benefit the most?

You should consider taking the supplement if you:

experience symptoms of deficiency, or you know you are deficient based on blood tests
don’t get enough iron from food (the easiest way to find out how much of this nutrient you are getting in your diet is to track your food intake for a while with Cronometer.com)
menstruate (most iron is lost through the blood, which significantly raises the need for iron in menstruating women)
are deficient in riboflavin (riboflavin is needed to absorb the mineral properly)
donate blood or bleed often
went through a gastric bypass surgery (it can lead to a deficiency in iron, as well as many other nutrients)
exercise a lot (exercise can lead to blood loss in the intestines)

Other types of iron supplements

The different types of iron supplements include:

Ferrous sulfate – This is the most popular supplemental type. Ferrous sulfate is cheap and generally suitable for vegans. However, this type often causes side effects that other types do not, such as oxidative stress in the intestines, bacterial overgrowth, constipation, and more. Ferrous sulfate is therefore not recommended.
Ferrous fumarate – This form is similar to ferrous sulfate.
Ferrous gluconate – This form contains less elemental iron than ferrous sulfate. However, some studies suggest that ferrous gluconate absorbs better and might be safer than ferrous sulfate.
Ferrous bisglycinate – Also known as ferrous amino acid chelate, this form is much safer than ferrous sulfate and absorbs just as well.
Heme iron polypeptide – This form is virtually identical to iron in meat and egg yolks. It is commonly sold under the name Proferrin ES.
Iron protein succinylate – In this form, iron is bound to compounds that prevent it from causing issues in the gastrointestinal tract. Its ability to prevent or treat anemia is not established.

Of all the types above, ferrous bisglycinate and heme iron polypeptide appear to be the best. Iron-saturated lactoferrin would be another great option but it is hard to obtain in most places.

Symptoms of iron deficiency

The most common signs of deficiency include:

pale skin
depression
fatigue
weakness
puffiness in the face and under the eyes
dizziness
lightheadedness
irregular heartbeat
muscle cramps
feeling cold in hands and feet
poor digestion
poor skin health
hypothyroidism
hair falling out
eyelashes falling out

Most of these are signs of anemia, a condition where the blood loses its capacity to carry oxygen to the tissues. Some of the symptoms of deficiency are related to hypothyroidism.

Keep in mind that these signs are just indications of a deficiency. If you experience some or even most of them, it does not necessarily mean you need more iron. On the other hand, some people may be deficient even though they are completely asymptomatic.

With that said, if you experience many or most of these symptoms, there is a high chance that you are not getting enough iron. The more of these symptoms you have and the more severe they are, the more likely you are to have a deficiency.

How much ferrous sulfate should you take?

To answer this question, you need to find out how deficient you are either through blood tests or by calculating how much iron you’re consuming in the diet.

The RDA (recommended daily allowance) for iron is 8 mg/d for men and 18 mg/d for women until the age of 50, after which it drops to 8 mg/d. Interestingly, the RDA for children is almost as high and sometimes higher than for adults, ranging from 7-15 mg/d.

These amounts should be enough for most people to avoid symptoms of deficiency. Most women need far less than 18 mg/d. The RDA is so high because some women produce considerably more menstrual fluid than usual. An average woman should get away with 8 mg/d. The RDA for pregnant and lactating women is 27 mg/d and 9 mg/d, respectively.

There are 2 types of iron: heme and non-heme.

Heme iron comes from meat and non-heme iron comes from plants and dairy. Heme iron is more bioavailable and absorbable than non-heme iron.

The RDA is based on an assumption that we absorb 16.8% of non-heme iron and 25% of heme iron, and that 90% of the iron we consume is non-heme. The RDA doesn’t consider the highly variable absorption of non-heme iron.

The absorption of the non-heme type is influenced by multiple factors. Vitamin C, citric acid and malic acid from fruit, lactic acid from fermented foods, and animal protein increase the absorption of non-heme iron. Vegetable protein, phytic acid, and many polyphenols lower the absorption.

This means you can increase the absorption of non-heme iron by consuming it along with fruit and animal protein. To absorb iron from grains, legumes, nuts, and seeds well, you will have to soak, sprout, or ferment these foods.

If you only consume non-heme iron, you need on average 5% more than the RDA. If you only consumed heme iron and no non-heme, you’d need about 30% less than the RDA.

For most people, 8 mg appears to be the best amount to shoot for. This amount should provide most of the benefits without meaningful side effects.

The upper safety limit is set at 45 mg/d. Higher doses may cause problems if you take the supplement for a prolonged period. Do not take more than this amount unless you have a great reason to do so.

The higher the dose you take, the higher the risk for side effects. Taking more than 10 mg daily should not be necessary and is not recommended unless you have a great reason to do so.

Food sources of iron

If most of your diet consists of whole foods, you are almost guaranteed to get enough iron.

The richest food sources are organ meats. As little as 50-100 grams of most types of organ meat provide more than enough iron for most people.

Red meat and fish usually provide enough in 200-400 grams. White meat only provides a very low amount. The same can be said about dairy and eggs.

Contrary to popular belief, it is very easy to get enough iron on a whole-food plant-based diet, even though the mineral is about 1.5 times harder to absorb.

Legumes, muscle meat, and most whole grains are also great sources. 100-250 grams of these foods give most people enough iron for the day.

Herbs, spices, nuts, seeds, and some iron-rich vegetables also provide a decent amount, although it would be hard to get enough iron from these sources alone. Most refined grains would lack iron naturally but they are fortified with this mineral.

Fruits, oils, sweets, and most vegetables only contain a very low amount. However, fruit can increase the absorption of iron in other foods.

The easiest way to find out how much iron you are getting in your diet is with Cronometer.com – this free app allows you to track all vitamins, minerals, and more.

Just keep in mind that heme iron from meat and eggs is approximately 1.5 times more bioavailable than the non-heme type from plants and dairy.

If you use cast iron cookware, beware that it can leach high amounts of iron into your food.

Best time to take ferrous sulfate

To absorb ferrous sulfate well, you want to take it with food. Taking the supplement with food is also better if it causes stomach upset when you take it on an empty stomach.

Whether you take the supplement in the morning or the evening doesn’t matter. It does not interrupt your sleep in any way.

It also doesn’t matter whether you take this mineral once a day or split it into smaller doses throughout the day. If anything, it is better to take the supplement less frequently.

Some things reduce the absorption of ferrous sulfate while some increase it. For example, most polyphenols, caffeine, phytic acid in nuts, seeds, grains, and legumes, and plant-based protein decrease the absorption while animal protein, vitamin C, and riboflavin increase it.

Interactions with other supplements

Riboflavin
Riboflavin is needed to absorb and utilize iron.
Vitamin C
Vitamin C (ascorbic acid) significantly increases the absorption of iron.
Citric acid
Just like vitamin C, citric acid from citrus fruits enhances iron absorption.
Copper
Copper and iron share many important functions in the body and need each other to work optimally.
EGCG
EGCG from green tea acts as an iron chelator and it can the mineral less absorbable. The same applies to many other compounds in tea, such as tannins.
Caffeine
Caffeine reduces the absorption of iron.
Turmeric
Turmeric can chelate iron, especially when excess is in the system.
Quercetin
Quercetin can also act as an iron chelator.
Calcium
300 mg of calcium carbonate or calcium phosphate reduces iron absorption by 15-50% when taken together with this mineral.

Where to buy ferrous sulfate

Amazon seems to be the best option for ordering ferrous sulfate supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.

Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.

FAQ

You can take the supplement daily and do not need to cycle it. Interestingly, those who take this mineral every other day as opposed to every day seem to experience headaches as a side effect less frequently.

All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, to dose them correctly, you may need a highly accurate scale (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatine, which rarely comes from an ethical source.

Yes. The supplement doesn’t impact your sleep in any negative way in the short term.

Ferrous sulfate supplements should not become harmful once they exceed the expiration date, but they can lose potency over time.

Keep the supplements in a cold, dark, and dry place, and they should remain just as potent for many months or even years.

Definitely. While getting enough iron is vital for optimal health, getting too much is just as common and can be just as harmful as too little. Iron overload often leads to symptoms similar to a deficiency, such as dizziness, fatigue, depression, and hair falling out. On top of this, too much iron can cause high cholesterol, diabetes, pain in the joints, chest, or abdomen, and faster aging. It also contributes to Alzheimer’s and Parkinson’s disease. If you were to experience these symptoms but kept consuming high amounts of iron, it would eventually cause hemochromatosis. This condition can cause serious liver damage and heart problems. The best way to prevent toxicity (besides not consuming excessive amounts of this mineral through diet and supplements) is by donating blood. Bleeding and donating blood can quickly and reliably rid you of excess iron.

Of all the types, ferrous bisglycinate and heme iron polypeptide appear to be the best. Iron-saturated lactoferrin would be another great option but it is hard to obtain in most places.

The most common reason people become deficient is that they don’t get enough of this nutrient from their diet. However, many things can hurt your iron status and increase your need for this nutrient. Most of these are related to blood loss. Thus, people who donate blood and menstruate are at a significantly higher risk of deficiency.

You may need more of the nutrient if you:
– experience signs of deficiency, or know that you are deficient from blood tests
– don’t get enough from food (the easiest way to find out how much of this nutrient you are getting in your diet is to track your food intake for a while with Cronometer.com)
– exercise a lot (exercise can lead to blood loss in the intestines)
– menstruate (most iron is lost through the blood, which significantly raises the need for iron in menstruating women)
– donate blood or bleed often
– went through a gastric bypass surgery (it can lead to a deficiency in iron, as well as many other nutrients)

Iron from ferrous sulfate can stay in your system for a very long time. An average man without a deficiency has enough iron stored in the body for 3 years. An average woman has enough iron for about 6 months.

Most ferrous sulfate, fumarate, and gluconate supplements on the market are vegan-friendly but always check the label to be sure. When it comes to heme iron supplements, such as Proferrin ES, they are generally not vegan-friendly.

No, it doesn’t. The supplement does not interfere with fasting in any significant way. However, taking it with a meal is still better because dietary fat increases its absorption.

References

Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.

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