Turmeric: small capsule effects, and a spice nobody has tested

Almost everything measured about turmeric was measured in capsules, and mostly in people with diabetes. The clearest number: across 15 randomised trials in 855 adults with prediabetes or type 2 diabetes, curcumin or turmeric supplements lowered systolic blood pressure by 2.69 mmHg against control, with a 95% confidence interval of 3.84 to 1.55, and diastolic pressure did not change significantly. In 35 trials of adults with mixed health status the systolic drop was 2.02 mmHg. Twenty-seven trials in the same diabetic population found triglycerides down by about 14 mg/dL and LDL cholesterol down by about 6 mg/dL, and the review rated its own certainty low for every outcome. The one trial of turmeric as a spice is about iron: 0.5 g of the powder added to a rice meal did not reduce iron absorption in 10 healthy young women in Thailand. We found no human study of what cooking does to curcumin, and USDA holds a single record for the ground spice.

The numbers, per 100 g

How much is actually in it

• Of 2235 commercial turmeric samples analysed in 48 publications from six continents, 20.0% were adulterated (20.4% of spice samples, 22.0% of supplements). — 2235 commercial turmeric spice and supplement samples, 48 publications, 2000 to 2025 (n = 2235) Evidence C source
  Overall adulteration 20.0%; spice 20.4%; supplements 22.0%

What your body absorbs

• Adding 0.5 g of turmeric powder (50 mg polyphenols) to a rice-based meal did not reduce iron absorption in healthy young women. — healthy young women in Thailand, randomised crossover, stable-isotope iron absorption (n = 10 per experiment) Evidence B source
  Turmeric: no inhibition of iron absorption (P = 0.91); chili: -38% (6.0% vs 9.7%)
• In a randomised crossover trial, curcuminoids from a colloidal turmeric formulation were absorbed better from food matrices than from capsules: an oat-milk dairy analogue raised dose-normalised AUC by 76% and Cmax by 105%. — adults, randomised crossover, plasma pharmacokinetics over 24 h Evidence B source
  Dairy analogue AUC24h +76%, Cmax +105%; sports bar AUC +40%; probiotic drink AUC +35%; nectar and gummies bioequivalent to capsules
• Seven cases of acute hepatitis reported to Italian phytovigilance up to 2019 all involved high-bioavailability, high-dose curcumin formulations. — 7 Tuscan spontaneous reports plus 23 published case reports of hepatotoxicity after Curcuma longa supplements (n = 30) Evidence C source
  All 7 Italian cases with high-bioavailability, high-dose products; positive dechallenge in 16 of 23 published cases

What it does to your health

• In 15 RCTs (855 adults with prediabetes or type 2 diabetes) curcumin or turmeric supplements lowered systolic blood pressure by 2.69 mmHg versus control, with no significant change in diastolic pressure. — adults with prediabetes or type 2 diabetes, 15 RCTs, 16 treatment arms (n = 855) Evidence A source
  SBP WMD -2.69 mmHg (95% CI -3.84 to -1.55); DBP WMD -1.20 mmHg (95% CI -2.84 to 0.44), not significant
• Across 27 RCTs in prediabetes and type 2 diabetes, curcumin or turmeric supplements lowered triglycerides by about 14 mg/dL and LDL cholesterol by about 6 mg/dL, but the certainty of evidence was rated low for every outcome. — adults with prediabetes or type 2 diabetes, 27 RCTs, 31 arms Evidence A source
  TG WMD -13.73 mg/dL (95% CI -19.49 to -7.96); TC -5.24 (95% CI -9.42 to -1.07); LDL-C -5.72 (95% CI -8.62 to -2.82); HDL-C +2.14 (95% CI 1.08 to 3.20)
• In 20 RCTs of people with type 2 diabetes, turmeric or curcumin supplements reduced body weight by 1.9 kg and waist circumference by 1.9 cm, with no effect on BMI or waist-to-hip ratio, and the evidence certainty was low. — adults with prediabetes or type 2 diabetes, 20 RCTs, 8 to 36 weeks (n = 1387) Evidence A source
  Body weight WMD -1.9 kg (95% CI -2.9 to -0.9); waist circumference WMD -1.9 cm (95% CI -3.5 to -0.2); GRADE low
• The 20 trials behind the weight-loss estimate used doses from 80 mg/day (nano-curcumin) to 2100 mg/day (turmeric) for 8 to 36 weeks, so no single dose can be read from the pooled number. — adults with prediabetes or type 2 diabetes, 20 RCTs (n = 1387) Evidence A source
  Dose range 80 to 2100 mg/day; duration 8 to 36 weeks
• An umbrella review of 11 meta-analyses (99 RCTs, 5546 people with non-alcoholic fatty liver disease) found curcumin or turmeric lowered AST and ALT liver enzymes versus control. — adults with non-alcoholic fatty liver disease, 99 RCTs across 11 meta-analyses (n = 5546) Evidence A source
  AST ES -1.072 (95% CI -1.656 to -0.488); ALT ES -0.625 (95% CI -1.170 to -0.134)
• Across 35 RCTs in mixed adult populations, curcumin or turmeric supplements lowered systolic blood pressure by 2.02 mmHg and diastolic by 0.82 mmHg. — adults, mixed health status, 35 RCTs Evidence A source
  SBP WMD -2.02 mmHg (95% CI -2.85 to -1.18); DBP WMD -0.82 mmHg (95% CI -1.46 to -0.18)
• In 66 RCTs of adults, turmeric or curcumin supplements lowered C-reactive protein by 0.58 mg/L, TNF-alpha by 3.48 pg/mL and IL-6 by 1.31 pg/mL versus control. — adults, 66 RCTs Evidence A source
  CRP WMD -0.58 mg/L (95% CI -0.74 to -0.41); TNF-alpha -3.48 pg/mL (95% CI -4.38 to -2.58); IL-6 -1.31 pg/mL (95% CI -1.58 to -0.67)

Safety, limits and interactions

• Only 3 of 20 RCTs in people with diabetes reported side effects of turmeric or curcumin: stomach ache in two people on 80 mg/day nano-curcumin, and itching, vertigo and constipation on 1500 mg/day curcumin. — adults with prediabetes or type 2 diabetes, 20 RCTs (n = 1387) Evidence A source
  Side effects reported in 3 of 20 trials; gastrointestinal and itching at 80 to 1500 mg/day
• A pathology series of 11 patients (10 women, median age 58) attributed acute hepatitis to over-the-counter turmeric supplements, and liver tests normalised in all after stopping the supplement. — 11 patients with biopsy-proven liver injury attributed to turmeric supplements, retrospective archive review (n = 11) Evidence C source
  RUCAM probable in 8 and possible in 3; recovery in all after withdrawal
• Oxalate nephropathy with kidney failure was diagnosed in a 69-year-old man taking chronic turmeric supplements together with long-term antibiotics and diarrhoea. — one 69-year-old man, incidental kidney failure at routine check-up (n = 1) Evidence C source
  Biopsy-confirmed oxalate nephropathy; turmeric one of several contributing factors
• In a monitored provocation, 10 g/day of turmeric for 4 days did not change tacrolimus blood levels in a kidney-transplant patient. — one renal transplant patient aged around 70 on tacrolimus, prednisone and mycophenolate (n = 1) Evidence C source
  No change in tacrolimus plasma concentrations during or after 10 g/day turmeric for 4 days
• A systematic review of allergic contact dermatitis from supplements and cosmetics lists turmeric among the herbal extracts documented as sensitisers. — published cases of allergic contact dermatitis linked to supplements and topical products Evidence C source
  Turmeric named as a documented sensitiser; patch testing confirms sensitisation
• EFSA set an acceptable daily intake of 3 mg curcumin per kg body weight per day from a reproductive toxicity NOAEL of 250 to 320 mg/kg with a 100-fold uncertainty factor. Children aged 1 to 10 can exceed it at maximum use levels of the food colour. — general population; exposure estimates for children aged 1 to 10 in European countries Evidence E source
  ADI 3 mg/kg bw/day; about 210 mg/day for a 70 kg adult
• NCCIH states that conventionally formulated oral turmeric or curcumin is likely safe in recommended amounts for 2 to 3 months, while liver damage has been reported with high-bioavailability curcumin products. — general public, NIH consumer fact sheet updated April 2025 Evidence E source
  Position statement; no effect size

What people believe that the data does not support

• The EU health-claims register lists one curcumin claim, on normal joint function, and it is non-authorised, so no curcumin or turmeric claim is authorised in the EU. — EU register on nutrition and health claims, snapshot 2026-09-21 Evidence E source
  0 authorised, 1 non-authorised claim for curcumin

Who this works differently for

• In 12 RCTs of 1303 people with diabetes, curcumin or turmeric supplements did not change serum creatinine or blood urea nitrogen, while urea fell by 2.53 mg/dL. — adults with type 1 or type 2 diabetes, 12 RCTs (n = 1303) Evidence A source
  Creatinine WMD -0.01 mg/dL (95% CI -0.03 to 0.01); BUN -0.41 mg/dL (95% CI -3.15 to 2.33); urea -2.53 mg/dL (95% CI -4.09 to -0.96)
• In 10 human trials (531 participants) curcumin had no significant effect on global cognition in ageing adults, and adverse events were more frequent in the curcumin groups. — older adults in RCTs of curcumin and cognition, 10 human studies (n = 531) Evidence A source
  Global cognition SMD 0.14 (95% CI -0.78 to 1.07); working memory SMD 1.01 (95% CI 0.15 to 1.87)
• A US-born child developed an elevated blood lead level traced to contaminated turmeric bought abroad. — one paediatric patient in the USA (n = 1) Evidence C source
  Elevated blood lead level from imported turmeric
• A case report attributes dietary-induced liver injury in a woman at 23 weeks of pregnancy to turmeric, with no dose in the abstract and no rechallenge. — one pregnant woman presenting with itching and abnormal liver tests at 23 weeks 4 days (n = 1) Evidence C source
  Dietary-induced liver injury attributed to high-dose turmeric; improvement after dietary restriction
• NCCIH advises that turmeric supplements during pregnancy may be unsafe and that little is known about amounts above food levels while breastfeeding. — pregnant and breastfeeding women, NIH consumer fact sheet updated April 2025 Evidence E source
  Position statement; no effect size

The bottom line

The weight number needs its frame. In 20 trials of 1387 people with prediabetes or type 2 diabetes lasting 8 to 36 weeks, supplements took off 1.9 kg of body weight and 1.9 cm of waist, with no change in BMI, and the certainty was graded low. The doses ran from 80 mg a day of nano-curcumin to 2100 mg a day of turmeric, so no single dose can be read from the pooled number. In non-alcoholic fatty liver disease, an umbrella review of 11 meta-analyses covering 99 trials and 5546 people found lower AST and ALT, reported as standardised effect sizes rather than enzyme units, with trials overlapping across the reviews. Sixty-six trials in adults found C-reactive protein down by 0.58 mg/L, a biomarker rather than an illness. Brain claims do worse: across 10 trials in 531 older adults, curcumin had no significant effect on global cognition, and adverse events were more frequent in the curcumin groups. The EU register holds one curcumin claim, on joint function, and it is non-authorised, which means the evidence was judged insufficient rather than disproven. A colloidal turmeric formulation was absorbed better from an oat-milk drink than from capsules, with dose-normalised AUC up 76%, in a crossover trial that tested one proprietary product and gave no n in the abstract. One in five commercial samples is not what it says: of 2235 turmeric spice and supplement samples in 48 publications from 2000 to 2025, 20.0% were adulterated, with sampling that was not random. Who should be careful. The liver is the organ that shows up in the case reports. Seven cases of acute hepatitis reported to Italian phytovigilance up to 2019 all involved high-bioavailability, high-dose curcumin products. A pathology series of 11 patients, 10 of them women with a median age of 58, saw liver tests normalise in all after stopping the supplement, and it has no denominator, so it gives no incidence. NCCIH calls conventionally formulated turmeric likely safe in recommended amounts for 2 to 3 months and says liver damage has been reported with the high-bioavailability products. In the diabetes trials, only 3 of 20 reported side effects at all: stomach ache in two people on 80 mg a day of nano-curcumin, and itching, vertigo and constipation on 1500 mg a day of curcumin. EFSA set an acceptable daily intake of 3 mg curcumin per kg body weight for the food colour, about 210 mg a day for a 70 kg adult, from an animal reproductive toxicity study. Children aged 1 to 10 can exceed that intake at maximum use levels of the colour. In pregnancy, NCCIH says supplements may be unsafe, and one woman at 23 weeks developed liver injury that a case report attributes to turmeric, with no dose given. A single child in the USA had an elevated blood lead level traced to turmeric bought abroad. In 12 trials of 1303 people with diabetes, creatinine did not change, though one 69-year-old man on chronic turmeric supplements, long-term antibiotics and diarrhoea developed oxalate nephropathy. Turmeric is a documented contact sensitiser, mostly from topical exposure. We have one drug interaction record: 10 g a day of turmeric for 4 days did not change tacrolimus levels in one transplant patient, which excludes nothing about other drugs or longer use.

Sources

1. turm-dv2-18 · market survey synthesis
   A total of 48 publications representing 2235 commercial turmeric samples were included in the study. The overall adulteration rate was 20.0%, with spice samples having a slightly lower percentage of adulterated samples (20.4%) than dietary and food supplements (22.0%).
   Pharm Biol, 2026 · checked 2026-09-23
2. turm-dv2-11 · RCT crossover
   Three experiments were conducted in healthy young women (n = 10/study) to assess the effect of chili and turmeric on Fe absorption from a rice-based meal containing vegetables and iron fortified fish sauce in vivo...Turmeric (0.5 g dry powder, 50 mg polyphenols as gallic acid equivalents) did not inhibit iron absorption (P = 0.91)
   J Nutr, 2006 · checked 2026-09-23
3. turm-dv2-12 · RCT crossover
   The relative bioavailability of total curcuminoids was increased in all the food matrices compared to that in the capsule formulation. The dairy analogue showed the highest increase in dose-normalized AUC24 h (+76%, p < 0.0001) and Cmax (+105%, p < 0.0001).
   Food Funct, 2025 · checked 2026-09-23
4. turm-dv2-14 · case series review
   Seven cases of acute hepatitis occurring in Tuscany up to September 2019 are described. In all cases, hepatotoxicity was associated with Curcuma longa formulations with high bioavailability and high dosage of curcumin/curcuminoids.
   Br J Clin Pharmacol, 2021 · checked 2026-09-23
5. turm-dv2-01 · meta-analysis of RCTs
   Fifteen RCTs comprising 16 treatment arms (n = 855 participants) were included. Pooled results indicated that curcumin/turmeric supplementation significantly reduced SBP (WMD: -2.69 mmHg; 95% CI: -3.84 to -1.55; p < 0.001; I2 = 30.1%) compared to control groups...However, no significant effect was found on DBP (WMD: -1.20 mmHg; 95% CI: -2.84 to 0.44; p = 0.15; I2 = 84.3%)
   Endocrinol Diabetes Metab, 2026 · checked 2026-09-23
6. turm-dv2-02 · meta-analysis of RCTs
   Twenty-seven RCTs (31 arms) were included. Curcumin/turmeric supplementation significantly reduced triglycerides (WMD: -13.73 mg/dL; 95% CI: -19.49, -7.96), total cholesterol (WMD: -5.24 mg/dL; 95% CI: -9.42, -1.07), and LDL-C (WMD: -5.72 mg/dL; 95% CI: -8.62, -2.82) and increased HDL-C (WMD: 2.14 mg/dL; 95% CI: 1.08, 3.20)...The certainty of evidence (GRADE) was low for all outcomes.
   Lipids, 2026 · checked 2026-09-23
7. turm-dv2-04 · meta-analysis of RCTs
   Twenty randomized controlled trials (RCTs) were included in the meta-analysis. Pooled analysis displayed that supplementation with turmeric/curcumin significantly decreased body weight (WMD: -1.9 kg; 95% CI: -2.9 to -0.9...but no effects on body mass index and waist-to-hip ratio in people with T2DM
   Nutr Diabetes, 2025 · checked 2026-09-23
8. turm-dv2-05 · meta-analysis of RCTs
   The range dose of turmeric/curcumin was from 80 mg/day [44–48] to 2100 mg/day [49–51]. The duration of RCTs varied from 8 weeks [45, 49–53] to 36 weeks [31]
   Nutr Diabetes, 2025 · checked 2026-09-23
9. turm-dv2-07 · umbrella meta-analysis
   Findings of 11 meta-analyses of 99 randomized controlled trials comprising 5546 participants revealed that curcumin/turmeric supplementation reduced AST (ES = -1.072, 95% CI (-1.656, -0.488), p = 0.000), ALT (ES = -0.625, 95% CI (-1.170, -0.134), p = 0.014)
   Phytother Res, 2024 · checked 2026-09-23
10. turm-dv2-08 · meta-analysis of RCTs
    Finally, 35 RCTs out of 4182 studies were included. Our findings suggested that curcumin/turmeric supplementation significantly improved SBP (WMD: -2.02 mmHg; 95 % CI: -2.85, -1.18), DBP (WMD: -0.82 mmHg; 95 % CI: -1.46, -0.18)
    Clin Nutr ESPEN, 2024 · checked 2026-09-23
11. turm-dv2-09 · meta-analysis of RCTs
    Sixty-six RCTs were included in the final analysis. We observed that turmeric/curcumin supplementation significantly reduces levels of inflammatory markers, including CRP (WMD: -0.58 mg/l, 95 % CI: -0.74, -0.41), TNF-α (WMD: -3.48 pg/ml, 95 % CI: -4.38, -2.58), and IL-6 (WMD: -1.31 pg/ml, 95 % CI: -1.58, -0.67)
    Cytokine, 2023 · checked 2026-09-23
12. turm-dv2-06 · meta-analysis of RCTs
    Three of the twenty included RCTs reported few side effects. In the first RCT, Supplementation with 80 mg/d nano-curcumin led to stomachache in two people with T2DM [45]. Chuengsamarn et al. observed itching, vertigo, and constipation with 1500 mg/d curcumin supplementation [31]
    Nutr Diabetes, 2025 · checked 2026-09-23
13. turm-dv2-13 · case series
    We identified 11 patients via retrospective pathology archive review: 10 females (91%) and one male, with a median age of 58 years (range = 37-66 years)...All patients stopped ingesting turmeric supplements after presenting with liver injury, and four patients additionally received steroid therapy; liver function tests normalised in all patients.
    Histopathology, 2025 · checked 2026-09-23
14. turm-dv2-15 · case report
    He was diagnosed with oxalate nephropathy in the setting of chronic turmeric supplementation and chronic antibiotic therapy with associated diarrhea.
    J Bras Nefrol, 2024 · checked 2026-09-23
15. turm-dv2-16 · case report
    administration of 10 g/day of turmeric for 4 days, then 10 g/day of curry for 4 days and then 10 g/day of ginger for 4 days. No change in tacrolimus plasma concentrations during and after the implementation of the protocol was observed.
    Eur J Hosp Pharm, 2023 · checked 2026-09-23
16. turm-dv2-17 · case report review
    Key sensitizers include vitamin derivatives (tocopherol, phytonadione, ascorbic acid), herbal extracts (Ginkgo biloba, turmeric, St. John's Wort), and antioxidants (α-lipoic acid, resveratrol).
    Dermatitis, 2026 · checked 2026-09-23
17. turm-dv2-21 · agency opinion
    The Panel concluded that the present database supports an ADI of 3 mg/kg bw/day based on the NOAEL of 250-320 mg/kg bw/day from the reproductive toxicity study for a decreased body weight gain in the F2 generation observed at the highest dose level, and an uncertainty factor of 100. The Panel concluded that at the maximum levels of use, intake estimates for 1- to 10-year old children at the mean and the high percentile (95th) are above the ADI in some European countries.
    EFSA Journal 2010, Scientific Opinion on the re-evaluation of curcumin (E 100) as a food additive · checked 2026-09-23
18. turm-dv2-22 · fact sheet
    Conventionally formulated oral turmeric or curcumin (not modified to enhance bioavailability) is likely safe in the recommended amounts for up to 2 or 3 months...Many curcumin products with increased bioavailability are on the market, and liver damage has been reported in some people who have consumed these bioavailable formulations.
    NCCIH (NIH), Turmeric, updated April 2025 · checked 2026-09-23
19. turm-dv2-24 · regulatory register
    POL-HC-8504 Curcumin Curcumin contributes to the normal functioning of joints. -/- Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-8504, snapshot 2026-09-21 · checked 2026-09-23
20. turm-dv2-03 · meta-analysis of RCTs
    Twelve RCTs (n = 1303 participants) were included. Curcumin/turmeric supplementation did not significantly affect creatinine (WMD: -0.01 mg/dL, 95% CI: -0.03 to 0.01, p = 0.519) or BUN (WMD: -0.41 mg/dL, 95% CI: -3.15 to 2.33, p = 0.769)...However, urea levels were significantly reduced (WMD: -2.53 mg/dL, 95% CI: -4.09 to -0.96, p = 0.002).
    Endocrinol Diabetes Metab, 2026 · checked 2026-09-23
21. turm-dv2-10 · meta-analysis of RCTs
    Ten human studies include 531 participants. Overall, curcumin showed no significant effect on global cognitive outcomes compared to placebo (SMD = 0.14, 95 % CI: -0.78 to 1.07)...The incidence of adverse events was higher in the curcumin group than in the control group.
    J Prev Alzheimers Dis, 2025 · checked 2026-09-23
22. turm-dv2-19 · case report
    We describe a case of elevated BLL in a US-born paediatric patient from contaminated turmeric purchased abroad.
    BMJ Case Rep, 2025 · checked 2026-09-23
23. turm-dv2-20 · case report
    We hereby report a case of a pregnant patient who demonstrated atypical signs and symptoms of dietary-induced liver injury during pregnancy. She presented with itching at 23 weeks 4 days of pregnancy and had deranged liver function tests and was diagnosed with dietary-induced liver injury.
    Case Reports Hepatol, 2024 · checked 2026-09-23
24. turm-dv2-23 · fact sheet
    The use of turmeric supplements during pregnancy may be unsafe. Little is known about whether it's safe to use turmeric in amounts greater than those commonly found in food while breastfeeding.
    NCCIH (NIH), Turmeric, updated April 2025 · checked 2026-09-23