Only 3 out of 100 anti-inflammatory supplements have solid evidence. What the studies show about omega 3, curcumin and vitamin D

Of the hundreds of dietary supplements promoted as solutions to chronic inflammation, only three have actually been shown to be effective in human studies. It's the omega 3 essential fatty acids, curcumin and, in some cases, vitamin D, according to an extensive analysis published by Scientific American.

The global anti-inflammatory supplements market was valued at $9.3 billion in 2025 and is expected to reach nearly $20 billion by 2035, according to a Fact.MR report. Turmeric (in the form of curcumin) and omega 3 dominate this segment, and consumers are increasingly interested in natural options. But most products off the shelf, such as capsules, powders and tablets that promise to support immunity or reduce inflammation, are not backed by scientific evidence.

“Good” Inflammation and “Bad” Inflammation

The inflammation can be brief and beneficial, such as after a sprained ankle or a two-day fever from a mild flu. Both are part of the healing process. Or it can be a long-term, much more dangerous phenomenon: a chronic, low-grade inflammation that persists in the body for years without obvious symptoms, gradually affecting the cells.

Research over the past decade has linked this type of silent inflammation to serious conditions such as cardiovascular disease, Alzheimer's dementia, certain cancers and autoimmune diseases such as lupus.

Chronic inflammation differs from acute inflammation by the mechanism that maintains it. Immune cells and proteins that normally fight bacteria and viruses in the short term remain activated for months or years. Over time, this constant activity damages blood vessels, for example, by increasing atheromatous plaques on arterial walls and can lead to clots that block blood flow, increasing the risk of heart attack or stroke.

How to measure inflammation in the body

The most relevant clinical trials focus on biomarkers that researchers use to monitor inflammation in the body. These include C-reactive protein (CRP), produced by the liver during periods of active inflammation, and cytokines, chemical messengers such as interleukin-6 (IL-6) and tumor necrosis factor alpha, secreted by immune and fat cells.

However, the interpretation of these markers is not straightforward. “We don't have a universally accepted or standardized measurement,” said Frank Hu, head of the nutrition department at the Harvard TH Chan School of Public Health, quoted by Scientific American. Inflammation involves hundreds of different cell types and many signaling pathways, added Prakash Nagarkatti, director of the US National Center for Dietary Supplements and Inflammation. For this reason, it is difficult to prove how effective a supplement is in reducing inflammation.

Omega 3 fatty acids, the most studied

Of the hundreds of supplements tested for their effects on human health, omega 3 fatty acids have some of the most compelling evidence. The two main forms – eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) – are metabolized by the body into signaling molecules that intervene in inflammatory processes in the body and can reduce the production of substances involved in inflammation.

One of the largest studies on the subject, VITAL, followed more than 25,000 adults for about five years. In participants who rarely ate fish, omega-3 supplements led to a slight decrease in C-reactive protein (CRP), one of the most important markers of inflammation. In the same group, a reduction in the risk of myocardial infarction was also observed.

“The people who benefit the most from these supplements are those who start with a low intake,” pointed out Dr. JoAnn Manson, an endocrinologist at Harvard Medical School, who led the VITAL study.

Other smaller research has confirmed that omega 3 supplementation can reduce specific markers of inflammation, especially in people with conditions such as heart failure, Alzheimer's disease and kidney disease. A 2012 study showed that low doses, about 1.25 or 2.5 grams per day, lowered interleukin-6 levels by 10% and 12%, respectively, over four months. A similar group receiving placebo had a 36% increase in interleukin-6 over the same period.

Recent reviews indicate that moderate doses (1-3 g per day of EPA and DHA) are most consistent in results, but there is still no clear agreement on the optimal amount or duration of treatment. In healthy people with low levels of inflammation, the effects may be limited.

Changes in biomarkers usually occur within 3-8 weeks, and when there are symptoms such as joint pain, stiffness, their mitigation can be felt after 3-6 months of constant administration.

Vitamin D can be helpful, but it is not a panacea

Newer studies show that vitamin D does not have widespread effects on diseases such as cancer or diabetes, as was believed a few years ago. In contrast, there are data indicating benefits in some autoimmune conditions.

In the VITAL study, people who took vitamin D daily for five years had a 22% lower risk of developing autoimmune diseases such as rheumatoid arthritis, psoriasis and lupus.

“Vitamin D in high doses has the effect of calming inflammation. So conditions that are directly related to inflammation may benefit,” said Dr. JoAnn Manson.

Some laboratory studies have indicated that vitamin D can interfere with molecular pathways involved in inflammation and suppress the production of pro-inflammatory cytokines. In a small study of women with type 2 diabetes, a dose of 50,000 international units (IU) every two weeks reduced CRP and increased levels of IL-10, an anti-inflammatory molecule.

Another study in women with polycystic ovary syndrome (PCOS) showed that a combination of vitamin D and omega 3 lowered CRP. And a daily dose of 3,200 international units improved insulin sensitivity and liver function in patients with polycystic ovaries, although it did not affect inflammatory markers.

The VITAL study reported that participants who took vitamin D experienced a 19% drop in CRP at two years, but the difference disappeared after four years. Most participants already had normal vitamin D levels.

Very high doses of 40,000 or 50,000 units per week may be required for significant anti-inflammatory effects, but carry some risks, such as hypercalcemia. The recommended daily dose for adults is 600 IU. The American College of Rheumatology maintains a conditional recommendation against the use of supplements, instead promoting obtaining vitamins from food. Arthur M. Mandelin, a rheumatologist at Northwestern University Feinberg School of Medicine, states that he considers using vitamin D as therapy only for patients with demonstrated deficiencies.

Curcumin, effects comparable to those of usual anti-inflammatories

Curcumin, the pigment that gives turmeric its yellow color, is a third compound showing promise in the fight against chronic inflammation. Research has shown that it can influence the mechanisms involved in the body's inflammatory response.

The available data mostly come from small studies in people with pre-existing conditions, such as metabolic disorders or osteoarthritis. In some cases, the effects were comparable to those of common anti-inflammatories, such as ibuprofen.

“Many of these studies point to a possible benefit,” said Janet Funk, a professor of medicine and nutritional sciences at the University of Arizona, who reviewed the literature on the subject.

A review published in the specialist journal Nutrients, which included several meta-analyses, shows that in many cases, curcumin was associated with a decrease in markers of inflammation, such as CRP, IL-6 or TNF-alpha.

However, there are also results that do not confirm these effects. A Canadian study found no relevant changes in inflammation in people who had surgery. In addition, curcumin is poorly absorbed and quickly eliminated from the body, which limits its effect. Some formulas attempt to improve absorption but are not consistently used in small studies.

One concern is that some commercial turmeric and curcumin powders contain dangerous contaminants, including lead.

“People buy turmeric powder based on the color. Partly to give it a nicer color, manufacturers add lead chromate,” pointed out Janet Funk.

A study published in The Journal of Rheumatology tested how well certain combinations of curcumin, omega 3 and vitamin D were tolerated in people at risk of developing rheumatoid arthritis. The results showed that supplementation was well tolerated over four weeks, with 97% adherence and predominantly mild side effects (heartburn – 32%, predominantly fishy taste – 30%, bloating – 24%).

What hasn't been proven to work (yet)

Other substances often touted for their effects on inflammation, such as flavonoids in green tea and dark chocolate or resveratrol in red wine, are not well supported by studies. One of the explanations lies in the way they are absorbed: the body uses them in small amounts, and in the case of resveratrol, the substance is eliminated quickly.

There are also isolated results showing effects on cardiovascular health, but their interpretation is not straightforward. For example, in the case of cocoa flavonoids, the benefits can be difficult to separate from caloric intake when they come from chocolate consumption.

Regulatory and research issues

Dietary supplements are not evaluated according to the same rules as drugs. In the United States, manufacturers are not required to demonstrate the effectiveness of products before marketing. The situation is similar in Europe, including Romania, where supplements are legally classified as food products, not treatments, and do not have to prove clinical effects before reaching the market. Moreover, the body that regulates dietary supplements is not the National Agency of Medicines and Medical Devices in Romania. The process is not one of “approval” but of “notification”.

“Notifications are made at the Institute of Food Bioresources (IBA) and at the notifying institutions of the Ministry of Health, depending on the composition of the product. Until 2021, IBA had the right to make notifications for complex formulas – combinations of plants, vitamins, minerals, and since then, the law has changed and those from the Ministry of Health have taken over, through the regional centers of Public Health”, explained Dr. Biologist Tatiana Onisei, for the publication SmartLiving.ro.

Under these conditions, interest in large clinical trials remains low. Even when there are research initiatives, practical difficulties arise. The composition of supplements can vary from one batch to another, especially in the case of herbal products, where the concentrations depend on the source of the raw material and the way of processing.

What do the experts actually recommend?

Specialists recommend what serious medical studies have confirmed: a healthy and balanced diet. Mediterranean diets, rich in vegetables, whole grains, and low in fish and poultry, have been repeatedly shown to reduce chronic disease and improve overall health. Regular physical activity also helps.

“A lot of people think that they can just take a dietary supplement, pop a pill, and that it can replace a healthy diet. That's not true at all,” JoAnn Manson pointed out.

An analysis of the VITAL trial, published in JAMA Network Open in 2022, found that neither vitamin D3 nor omega 3 reduced the risk of frailty in healthy older adults.

In short, omega 3s, curcumin and, in some cases, vitamin D can alleviate chronic inflammation, especially in people with pre-existing conditions or nutritional deficiencies. But none of these supplements are a substitute for a balanced diet, regular exercise and regular medical check-ups.