Dietary supplements and fortified foods are used to ensure adequate dietary intake of important vitamins and minerals.

While dietary supplements and fortified foods can be helpful and even necessary, in many situations, they could lead to excessive nutrient intake and other negative side effects if consumed in excessive amounts.

This is because there are differences between the synthetic nutrients found in supplements and fortified foods and the nutrients naturally contained within the foods you eat.

This article explains the differences between natural and synthetic nutrients.

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Generally, synthetic nutrients refer to artificial nutrients found in dietary supplements and fortified foods.

In comparison, natural nutrients are nutrients like vitamins, minerals, fatty acids, and antioxidants found in foods, such as fruits, vegetables, fish, dairy, beans, grains, and meat.

Most nutrients found in dietary supplements are made through chemical processes to imitate the natural nutrients found in food.

Even though some supplements are made from whole food sources, such as vitamin C supplements made from fruit extracts, they typically contain a much higher dose of nutrients than found in a normal food serving.

Synthetic nutrients are consumed through dietary supplements and fortified foods. It’s reported that about 33% of adults in the United States take multivitamin supplements. Plus, many people supplement with isolated nutrients like vitamin D, zinc, vitamin C, iron, and B12 (1).

What’s more, many food products are fortified with synthetic nutrients like iron, calcium, copper, folic acid, and vitamin A (2).

Maintaining optimal nutrient levels is essential to health, but the consumption of fortified foods and dietary supplements may lead to the excessive consumption of certain nutrients (1, 2).

Plus, the body absorbs some synthetic nutrients more easily than their natural counterparts. Many supplements and fortified foods also contain very high doses of vitamins and minerals that typically aren’t necessary for most people.

Taking in high doses of specific nutrients from supplements or fortified foods, especially over long periods of time, could lead to adverse health effects (1).

Summary

Natural nutrients are naturally contained within foods like fruits, vegetables, and eggs, while synthetic nutrients are found in dietary supplements and fortified foods.

While synthetic nutrients are designed to mimic the natural nutrients found in food, research has demonstrated significant differences between synthetic and natural nutrients.

Absorbability

Studies show that while the absorbability of some synthetic nutrients is similar to that of naturally derived nutrients, others can be more or less bioavailable to the body.

For example, while vitamin C has been shown to have similar bioavailability when consumed naturally through foods like fruits and vegetables and supplements with synthetic vitamin C, other synthetic nutrients are more bioavailable (3, 4, 5).

One example is folic acid. Folic acid is a synthetic nutrient that’s much more bioavailable than the natural folate found in foods.

The naturally occurring folate found in food has an absorbability of around 50%. However, when consumed on an empty stomach, synthetic folic acid is thought to have 100% absorbability, while folic acid found in fortified foods is thought to have 85% absorbability (6).

Due to the difference in the absorption rates between folic acid and folate, dietary folate equivalents (DFEs) were developed (6):

1 mcg of DFEs = 1 mcg of naturally occurring folate in food = 0.5 mcg folic acid taken in supplement form on an empty stomach = 0.6 mcg folic acid ingested with foods

Additionally, when taken in supplement form on an empty stomach, some nutrients are much more bioavailable than when consumed as part of a mixed meal from natural food sources.

This is because certain nutrients and compounds found in mixed meals inhibit the absorption of other nutrients, making them less bioavailable.

Iron is an example of a nutrient that has higher bioavailability when taken as a single nutrient on an empty stomach compared with when consumed through the diet (7, 8).

Risk of overconsumption

Although supplements and fortified foods can be beneficial and necessary for certain people to correct or prevent deficiency, the overconsumption of synthetic nutrients can lead to excessive intakes of certain vitamins and minerals.

While it’s technically possible to overconsume nutrients from food sources, dietary supplements and fortified foods are the main causes of excessive nutrient intake.

This is because supplements and fortified foods typically contain much higher amounts of nutrients than whole foods. Plus, certain nutrients, such as folic acid, are much more readily absorbed than nutrients from whole foods.

For example, studies have shown that people who consume fortified foods or take dietary supplements are more likely to exceed the tolerable upper intake level (UL) for nutrients like zinc, folic acid, and vitamin A (9).

One study found that children who consumed more foods fortified with nutrients, including copper, vitamin A, folic acid, zinc, and selenium, were at a greater risk of exceeding the UL for these nutrients (2).

The same study found that adults who frequently consumed fortified foods were more likely to exceed the UL for calcium and iron (2).

Studies have also shown that people who take dietary supplements are more likely to exceed the UL for some nutrients, including calcium, zinc, iron, magnesium, and folic acid (10, 11).

Research suggests that the risk of excessive intake of nutrients is most common in supplement users in high income countries (9).

However, just because someone exceeds the UL for a certain nutrient doesn’t necessarily mean that their health is at risk.

Upper levels of intake (ULs) are not meant to be used as rigid cutoff points. Rather, they help ensure that nutrient intake levels don’t exceed a safe level for most people (12).

Summary

Some synthetic nutrients are more absorbable than the natural nutrients in foods. Plus, fortified foods and supplements typically contain higher amounts of nutrients than natural foods. This could lead to the excessive consumption of certain nutrients.

Even though fortified foods and dietary supplements are necessary to treat or prevent deficiency in some people, synthetic nutrients may have negative side effects.

The following are examples of dietary supplements that have been linked to negative health outcomes. This list is not exhaustive, and other synthetic nutrients may have been associated with adverse effects, although they’re not listed.

Vitamin E

Supplemental vitamin E may be necessary for certain groups of people, including people with medical conditions that affect fat absorption. However, high-dose supplemental vitamin E isn’t appropriate for most and has been linked to adverse health effects.

For example, supplemental vitamin E has been associated with an increased risk of cancer in certain populations.

A study that included data on 35,533 healthy men found that vitamin E supplements significantly increased the risk of prostate cancer. Men who took vitamin E supplements had a 17% greater risk of developing prostate cancer than men who took a placebo (13, 14).

Furthermore, high-dose supplemental vitamin E may lead to an increased risk of bleeding (15).

Vitamin A and beta carotene

Research has linked supplemental vitamin A and beta carotene to an increased risk of certain cancers.

A review of 49 studies found that supplementation with vitamin A was associated with a 16% higher risk of cancer. It also found that when taken on its own in supplemental form, beta carotene was associated with a 6% increased risk of death from all causes (16)

Beta carotene is a provitamin A, which means that it gets converted into vitamin A in the body. Beta carotene supplements have also been shown to significantly increase the risk of lung cancer in people who smoke (17).

Plus, high vitamin A levels from taking high-dose supplements have been associated with low bone mineral density and increased fracture risk in women, especially among women with low vitamin D levels (18).

Consuming too much preformed vitamin A (not beta carotene) from dietary supplements can also lead to toxicity, which can be fatal (19).

Calcium

Many people consume supplemental calcium in hopes of supporting bone health. Even though supplemental calcium may be appropriate under certain circumstances, high-dose supplementation may lead to complications.

A review of 42 studies found that while calcium from food sources did not increase the risk of heart disease, calcium supplements might increase heart disease and heart attack risk (20).

The review found that the use of calcium supplements increased the risk of heart disease and heart attacks by as much as 20% and 21%, respectively (20).

A recent review of 13 double-blind, randomized controlled trials found that calcium supplements were associated with a 15% increased risk of heart disease in healthy postmenopausal women (21).

This is because having elevated calcium levels may contribute to the calcification of arteries, a known risk factor for heart disease (22).

Folic acid

Unlike the folate naturally found in food, folic acid from supplements and fortified foods has been associated with an increased risk of certain health conditions.

Due to the high absorption rate of folic acid, taking in large doses of folic acid (over 400 mcg per day) from supplements or fortified foods may lead to high levels of unmetabolized folic acid (UMFA) in the blood (23).

One study found week evidence linking high maternal UMFA blood levels to an increased risk of autism spectrum disorder (ASD) among their offspring (24).

Further research is needed to verify the relationship between maternal UMFA blood levels and ASD.

High-dose folic acid supplements have also been linked to accelerated cognitive decline in older adults with low B12 levels, which is very common in this population. They may alter the immune response in healthy adults and older women (25, 26, 27).

Additionally, a large review of meta-analyses found that having high blood folate levels was associated with an increased risk of prostate cancer. However, more research in this area is needed (28).

Summary

Synthetic nutrients from supplements and fortified foods may have deleterious effects on health, especially when used in high doses.

Dietary supplements and fortified foods could lead to the excessive consumption of certain nutrients and adverse health effects, but supplements and fortified foods are beneficial in many cases.

Studies show that many people have suboptimal intakes of certain nutrients, and deficiencies in certain vitamins and minerals are more common in some populations.

For example, one study that analyzed data from 26,282 U.S. adults found that a large portion of the study population had nutrient intakes below the current estimated average requirements (EARs), which are the nutrient levels estimated to meet the needs of 50% of the population.

The study found that 45% of adults had inadequate vitamin A intake, 15% for zinc, 46% for vitamin C, 84% for vitamin E, and 95% for vitamin D, all of which are nutrients that are critical for immune system health (29).

The researchers suggested that dietary supplements may help fill these nutrient gaps (29).

In addition to the nutrients listed above, calcium, potassium, choline, magnesium, iron, and B12 are commonly underconsumed by the U.S. population (29, 30, 31, 32, 33, 34).

This may be due to various factors, including unhealthy eating patterns, lack of food variety, and lack of access to healthy foods.

Another study including 10,698 adults grouped by income level found that the use of dietary supplements in addition to normal dietary intake was associated with increased nutrient intakes and a decreased risk of nutrient inadequacy, compared with dietary nutrient intake alone (35).

Even though supplements improved nutrient intakes in all groups, the greatest benefits were seen in adults who scored slightly higher on income status, who had a lower prevalence of micronutrient inadequacy than those in the lower income groups (35).

Adults with lower socioeconomic status had a higher prevalence of vitamin and mineral inadequacies (35).

Fortified foods have also been shown to benefit health. For example, folic acid fortification has been shown to increase folate levels in pregnant women and decrease the risk of neural tube defects in their offspring (36).

Plus, studies show that dietary supplements and fortified foods help contribute to higher intakes of commonly underconsumed nutrients like thiamine, iron, folate, and vitamins A, C, and D (12).

Who should consider supplements and fortified foods

The healthiest way to take in the nutrients your body needs is to consume a well-rounded diet that’s rich in whole foods and low in highly processed foods.

However, many groups would likely benefit from supplements or fortified foods, including:

  • children and teens
  • people following restrictive diets
  • pregnant and breastfeeding women
  • older adults
  • people with certain medical conditions
  • those who don’t have access to fresh and healthy foods

For example, pregnant and breastfeeding women have an increased need for many nutrients, including B12, choline, folate, calcium, iron, and vitamin D. They’re encouraged to take prenatal dietary supplements before, during, and after pregnancy and breastfeeding (37).

Furthermore, older adult populations are more likely to be deficient in nutrients like B12 and vitamin D, which may significantly affect health. This is why experts recommend that older adults are screened for deficiencies and supplemented accordingly (33, 38).

Additionally, people with conditions like autoimmune diseases, anemia, and cancer, as well as those who have a poor dietary intake or follow restrive diets, often depend on supplements and fortified foods to prevent deficiency (39, 40, 41, 42, 43).

That said, many multivitamin supplements and fortified foods, unfortunately, contain high amounts of nutrients that have the potential of being overconsumed when used in addition to normal dietary intake.

For this reason, it’s best to use targeted nutrient supplementation to treat and prevent inadequacies and deficiencies when possible, rather than treatment with multinutrient supplements that contain large doses of most vitamins and minerals (44).

Summary

Supplementation and the use of fortified foods are beneficial and necessary for many people, including pregnant and breastfeeding women, people on restrictive diets, those with medical conditions, and older people.

Natural nutrients are found within the foods we eat, while synthetic nutrients are found in dietary supplements and fortified foods.

Although synthetic nutrients are created to mimic natural nutrients, there are differences between the two, including their bioavailability and the potential for overconsumption.

While some synthetic nutrients have been associated with adverse health effects, dietary supplements and fortified foods are necessary for many people.

To reduce the risk of potential complications due to overconsuming synthetic nutrients, it’s best to prevent and treat inadequacies and deficiencies using targeted nutrient interventions rather than high-dose multinutrient supplements.