Carrots and parsnips: the capsule that failed the vegetable

Start with the strongest evidence, because it is about capsules and not about carrots. In a meta-analysis of 8 randomized trials in 167,141 adults given 15 to 30 mg of beta-carotene a day, lung cancer rose 16 percent (RR 1.16, 95% CI 1.06 to 1.26). Among smokers and asbestos workers it rose 21 percent (RR 1.21, 95% CI 1.08 to 1.35). A second meta-analysis of 31 trials in 216,734 adults found no change in all-cause mortality (RR 1.02, 95% CI 0.98 to 1.05) and 14 percent more lung cancer deaths (RR 1.14, 95% CI 1.02 to 1.27). Those trials tested an isolated supplement and not a vegetable, and no record on this page says how much beta-carotene a carrot or a parsnip holds. Whole carrots point the other way in observational data. Pooling 50 prospective studies with 52,000 cancer cases, the highest carrot intake went with about 10 percent lower cancer incidence (RR 0.90, 95% CI 0.87 to 0.94), and plasma alpha-carotene as a marker of carrot eating gave RR 0.80 (95% CI 0.72 to 0.89). Those are associations, and the reviewers say plainly that nobody knows which compound is responsible, since the obvious candidate failed in the trials above. One thing to carry into the rest of the page: almost every record here is about carrots. Parsnip appears only in the furocoumarin evidence and in a single case report.

How much is actually in it

• In two randomized crossover feeding studies, lycopene from red carrots was about 44% as bioavailable as lycopene from tomato paste. — 9 and 10 adults, 11 days per treatment with 10-day washouts, carrots delivering 2.6 to 5 mg lycopene daily (n = 19 across two studies) Evidence B source
  Lycopene in red carrot about 44% as bioavailable as in tomato paste; serum lycopene plateau at or above 20 mg per day
• Carrot is named among the vegetables whose ingestion can pose a health risk on thallium-contaminated soil, with derived soil thresholds of 3.77 to 14.43 mg per kg. — 35 vegetable species in a meta-analysis of soil and plant thallium measurements (n = 35 species) Evidence D source
  Soil thallium thresholds for carrot 3.77 to 14.43 mg per kg, versus 0.24 to 4.89 for kale and 2.94 to 3.32 for lettuce

What a real portion looks like

• In a randomized crossover study of 30 adults, calcium absorption per 3.5 oz (100 g) of carrot was 41% higher from a carrot line engineered to carry more of a calcium transporter. — 15 male and 15 female adults in a crossover study with dual stable calcium isotopes (n = 30) Evidence B source
  Total calcium absorption per 3.5 oz (100 g) of carrots 41% plus minus 2% higher from sCAX1 carrots than from control carrots
• US adults take in about 81 micrograms of furocoumarins a day, and higher intake showed only a statistically non-significant trend toward melanoma history. — US adults in NHANES 2003 to 2012, 75 with a reported melanoma history (n = NHANES 2003 to 2012) Evidence C source
  Mean intake 81.4 micrograms per day, standard error 5.5; melanoma OR 1.75, 95% CI 0.43 to 7.20 for the top 10 percent of intake

What your body absorbs

• In a randomized crossover trial in 16 adults, beta-carotene was about three times more bioavailable from papaya than from an equal dose in raw carrots. — 16 healthy adults, test meals matched for beta-carotene and lycopene, 9.5 hours of sampling (n = 16) Evidence B source
  Beta-carotene bioavailability from papaya about 3 times that from carrots and tomatoes; carrots and tomatoes did not differ

What cooking and storage change

• In a randomized crossover trial in 7 adults, carotenoids from a carrot salad barely reached the blood with a fat-free dressing, and absorption rose stepwise with 6 g and then 0.99 oz (28 g) of oil in the dressing. — 7 adults eating salads of spinach, romaine, cherry tomatoes and carrots with 0, 6 or 28 g canola oil (n = 7) Evidence B source
  Appearance of alpha-carotene, beta-carotene and lycopene in chylomicrons negligible with fat-free dressing; higher with reduced-fat, P < 0.04; higher again with full-fat, P < 0.02
• Only about 5% of the all-trans beta-carotene in a carrot puree meal reached the micellar phase of the human duodenum, against 5.6% for lutein and 2.0% for lycopene. — 10 healthy men fed three liquid test meals with 40 g sunflower oil, 3 weeks apart (n = 10) Evidence C source
  All-trans beta-carotene in micellar phase 4.7% plus minus 0.3%; lutein 5.6% plus minus 0.4%; lycopene 2.0% plus minus 0.2%

What it does to your health

• Observational data link the highest carrot intake to about 10% lower cancer incidence across 50 prospective studies and 52000 cases. — Pooled prospective cohorts recording carrot intake (n = 50 prospective studies, 52000 cases) Evidence C source
  RR 0.90, 95% CI 0.87 to 0.94; plasma alpha-carotene as a carrot biomarker gave RR 0.80, 95% CI 0.72 to 0.89
• By meta-analysis of 8 randomized trials in 167141 people, beta-carotene supplements raised lung cancer risk by 16%, and by 21% in smokers and asbestos workers. — Adults without lung cancer at baseline in 8 randomized trials, 15 to 30 mg beta-carotene daily (n = 167141) Evidence A source
  RR 1.16, 95% CI 1.06 to 1.26 overall; RR 1.21, 95% CI 1.08 to 1.35 in smokers and asbestos workers
• By meta-analysis of 31 randomized trials in 216734 adults, beta-carotene supplements did not lower overall mortality and raised lung cancer mortality by 14%. — Adults of any health condition, median age 60 years, median treatment 3 years and follow-up 4.6 years (n = 216734) Evidence A source
  All-cause mortality RR 1.02, 95% CI 0.98 to 1.05; lung cancer mortality RR 1.14, 95% CI 1.02 to 1.27; HIV-related mortality RR 0.55, 95% CI 0.33 to 0.92

Safety, limits and interactions

• A systematic review of 19 epidemiological studies found moderate evidence that a diet high in furocoumarins, the phototoxic compounds concentrated in parsnip and other Apiaceae roots, raises cutaneous melanoma risk. — 20 publications based on 19 epidemiological studies of dietary furocoumarin intake and melanoma (n = 19 studies) Evidence C source
  Moderate qualitative evidence of higher melanoma risk; no pooled estimate because of heterogeneity in exposure assessment

What people believe that the data does not support

• The EU refused the right to claim that beta-carotene is an antioxidant that protects the body cells from free radicals and oxidation. — EU Register on nutrition and health claims, 2330 claims, 262 authorized (n = 1 claim) Evidence E source
  Status Non-authorized
• The EU refused the right to claim that beta-carotene helps support immunity or skin immune responses under UV radiation from sun exposure. — EU Register on nutrition and health claims, 2330 claims, 262 authorized (n = 1 claim) Evidence E source
  Status Non-authorized

Who this works differently for

• A reported case of systemic allergic contact dermatitis was traced to Apiaceae root vegetables, with patch tests positive to parsnip, carrot and celeriac and negative to falcarinol. — One adult woman with rhinitis, conjunctivitis, stomatitis and hand dermatitis (n = 1) Evidence D source
  Positive prick and patch tests to celeriac, parsnip and carrot; negative to falcarinol, so the allergen stays unidentified
• Observational data link the highest dietary beta-carotene intake to 37% lower risk of depression across 25 studies and about 101000 participants. — 25 observational studies, 24 cross-sectional or case-control and 1 prospective cohort, 100955 participants (n = 100955) Evidence C source
  RR 0.63, 95% CI 0.55 to 0.72, P < 0.001 for highest vs lowest dietary beta-carotene intake
• In people with phenylketonuria, serum beta-carotene was higher in those taking their amino acid formula regularly, at 74.4 against 53.2 nanograms per milliliter. — 68 people with classical PKU aged 6 to 41 with full fat-soluble vitamin panels (n = 68 of 98) Evidence C source
  Beta-carotene 74.40 (56.70 to 98.45) vs 53.20 (34.10 to 68.60) ng/mL, p = 0.003; pooled meta-analysis found no difference by adherence

What is still unknown

• Nobody knows which compound makes carrots track with lower cancer rates, because beta-carotene, the obvious candidate, failed in controlled trials and polyacetylenes remain untested in humans. — Evidence base of 198 observational studies on carrot intake and cancer (n = 198 observational studies) Evidence C source
  Carrot intake associated with lower cancer risk while beta-carotene shows no benefit in controlled trials; causal mechanism unresolved

The bottom line

Fat is the practical fact about carrots. In a crossover trial in 7 adults eating a salad of spinach, romaine, cherry tomatoes and carrots, carotenoids barely appeared in the blood with a fat-free dressing. They rose with 6 g of canola oil in the dressing (P < 0.04) and rose again with 28 g (P < 0.02). Seven people is very few, and the effect is large enough to see anyway. The mechanism sits one step earlier. In 10 men fed carrot puree with sunflower oil, only 4.7 percent of the all-trans beta-carotene reached the micellar phase in the duodenum, against 5.6 percent for lutein and 2.0 percent for lycopene, in a non-randomized challenge. Matrix matters as much as dose. Beta-carotene was about three times more available from papaya than from an equal amount in raw carrots in 16 adults, which the authors put down to how the pigment is packed inside the plant cell. Two numbers here describe bred or engineered carrots rather than the ones in the shop. A carrot line carrying more of a calcium transporter gave 41 percent more absorbed calcium per 3.5 oz (100 g) than its control in 30 adults. Lycopene from red carrots, a selected variety, was about 44 percent as available as lycopene from tomato paste across two studies in 19 adults. Neither of them is a portion. This page holds no serving size for carrot or for parsnip at all. Caution belongs mostly to the parsnip. Furocoumarins, the phototoxic compounds concentrated in parsnip and other Apiaceae roots, were reviewed across 19 epidemiological studies, which gave moderate evidence of higher cutaneous melanoma risk and no pooled number, because exposure was measured in ways that could not be combined. US adults take in about 81.4 micrograms of furocoumarins a day. In NHANES the top tenth of intake carried an odds ratio of 1.75 for a melanoma history (95% CI 0.43 to 7.20) on only 75 cases, an interval so wide that the useful part is the exposure figure. One woman developed systemic allergic contact dermatitis with positive patch tests to parsnip, carrot and celeriac and a negative test to falcarinol, which names the plant family and leaves the allergen unidentified. On thallium-contaminated soil carrot is listed among the vegetables that can pose a risk, with derived soil thresholds of 3.77 to 14.43 mg per kg against 0.24 to 4.89 for kale and 2.94 to 3.32 for lettuce, which means carrot takes up thallium less readily than those two. No record on this page covers pregnancy, children or drug interactions for either root. The label myths are both about beta-carotene. The EU refused the claim that it is an antioxidant protecting body cells from free radicals, and refused the claim that it supports skin immune responses under UV, which is the one behind the idea that carrots prepare skin for the sun. All eight beta-carotene claims in that register were rejected. Two groups differ, and one question stays open. Across 25 studies in 100,955 people, the highest dietary beta-carotene intake went with 37 percent lower risk of depression (RR 0.63, 95% CI 0.55 to 0.72). The data is cross-sectional in 24 of the 25, where depression changing the diet is at least as plausible as the reverse. In 68 people with classical phenylketonuria, serum beta-carotene was higher in those taking their amino acid formula regularly, 74.4 against 53.2 nanograms per milliliter (p = 0.003). That is a group whose carotenoid status rides on a formula rather than on vegetables, and the authors call the certainty very low. Across 198 observational studies the association between carrots and lower cancer rates holds while the responsible compound stays unknown, because beta-carotene failed in controlled trials and the polyacetylenes have never been tested in people.

Sources

1. carpar-daily-r3-08 · RCT crossover, bioavailability
   Making inferences from both studies, the lycopene in the red carrot is about 44% as bioavailable as that from tomato paste.
   Eur J Clin Nutr, 2004 · checked 2026-09-25
2. carpar-daily-r3-12 · environmental meta-analysis
   The soil Tl thresholds for kale, lettuce and carrot were in the range of 0.24-4.89, 2.94-3.32 and 3.77-14.43 mg/kg, respectively. Ingestion of kale, beet, sweet potato, potato, taro, pepper, turnip, Chinese cabbage, eggplant and carrot poses potential health risks.
   Sci Total Environ, 2024 · checked 2026-09-25
3. carpar-daily-r3-07 · RCT crossover, isotope
   In a cross-over study of 15 male and 15 female adults, we found that when people were fed sCAX1 and control carrots, total calcium absorption per 100 g of carrots was 41% +/- 2% higher in sCAX1 carrots.
   Proc Natl Acad Sci U S A, 2008 · checked 2026-09-25
4. carpar-daily-r3-10 · cross-sectional survey analysis
   Mean total intake of the selected furocoumarins among US adults was 81.4 μg/day (standard error = 5.5). ... Furocoumarins are widely consumed among US adults, and a trend towards higher odds of melanoma history was observed among those with higher furocoumarin intake, although this relationship was not statistically significant.
   Nutr Cancer, 2020 · checked 2026-09-25
5. carpar-daily-r3-05 · RCT crossover, bioavailability
   The bioavailability of β-carotene from papayas was approximately three times higher than that from carrots and tomatoes, whereas differences in the bioavailability of β-carotene from carrots and tomatoes were insignificant.
   Br J Nutr, 2014 · checked 2026-09-25
6. carpar-daily-r3-04 · RCT crossover, absorption
   After ingestion of the salads with fat-free salad dressing, the appearance of alpha-carotene, beta-carotene, and lycopene in chylomicrons was negligible.
   Am J Clin Nutr, 2004 · checked 2026-09-25
7. carpar-daily-r3-06 · controlled feeding study
   The proportion of all-trans carotenoids found in the micellar phase of the duodenum was as follows (means +/- SE): lutein (5.6 +/- 0.4%), beta-carotene (4.7 +/- 0.3%), lycopene (2.0 +/- 0.2%).
   Am J Physiol Gastrointest Liver Physiol, 2003 · checked 2026-09-25
8. carpar-daily-r3-01 · meta-analysis of prospective studies
   Of 198 observational studies, in 50 prospective studies with 52000 cases recording carrot intake, the cancer-risk was substantially reduced (RR 0.90, 95% CI 0.87-0.94, p ˂ 0·00004).
   Crit Rev Food Sci Nutr, 2025 · checked 2026-09-25
9. carpar-daily-r3-02 · meta-analysis of RCTs
   The findings indicate that beta-carotene supplementation was associated with an increased risk of lung cancer (RR = 1.16, 95% CI = 1.06-1.26). This effect was even more noticeable among smokers and asbestos workers (RR = 1.21, 95% CI = 1.08-1.35) and non-medics (RR = 1.18, 95% CI = 1.07-1.29).
   Nutrients, 2022 · checked 2026-09-25
10. carpar-daily-r3-03 · meta-analysis of RCTs
    In a random-effects meta-analysis of all 31 trials, beta-carotene supplements were found to have no preventive effect on mortality (risk ratio 1.02, 95% confidence interval 0.98-1.05, I 2 = 42%). ... Instead, beta-carotene supplementation significantly increased the risk of lung cancer mortality (RR 1.14, 95% CI 1.02, 1.27, I 2 = 3%) but decreased the risk of human immunodeficiency virus-related mortality (RR 0.55, 95% CI 0.33, 0.92, I 2 = 0).
    Front Med (Lausanne), 2022 · checked 2026-09-25
11. carpar-daily-r3-09 · qualitative systematic review
    In a qualitative synthesis, we found moderate evidence supporting the notion that dietary furocoumarin intake at higher levels acts as a risk factor for cutaneous melanoma.
    Nutrients, 2025 · checked 2026-09-25
12. carpar-daily-r3-13 · EU health claim register entry
    POL-HC-6702 Beta-Carotene Is an antioxidant that protects the body’s cells. Can protect you from free radicals. Can protect your cells and tissues from oxidation. Can contribute to the total antioxidant capacity of the body. Protects the body's cells. Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6702, snapshot 2026-09-21 · checked 2026-09-25
13. carpar-daily-r3-14 · EU health claim register entry
    POL-HC-6699 Beta-Carotene Beta-carotene helps to support immunity upon UV-radiation (sun exposure) Helps to maintain healthy immune responses upon UV-radiation (sun exposure) Helps to maintain physiological immune responses of the skin upon UV radiation (sun exposure) Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6699, snapshot 2026-09-21 · checked 2026-09-25
14. carpar-daily-r3-11 · case report
    The patient was contact-sensitive to celeriac, parsnip, and carrot, but tested negative to falcarinol.
    Contact Dermatitis, 2014 · checked 2026-09-25
15. carpar-daily-r3-15 · meta-analysis of observational studies
    On the other hand, the overall multi-variable adjusted RR indicated that dietary beta-carotene intake was negatively associated with depression (RR = 0.63, 95%CI: 0.55-0.72; P < 0.001).
    Front Nutr, 2022 · checked 2026-09-25
16. carpar-daily-r3-16 · cross-sectional study with meta-analysis
    Beta-carotene was elevated with regular intake (74.40 [56.70-98.45] vs. 53.20 [34.10-68.60] ng/mL, p = 0.003). ... No differences were observed for vitamin E or beta-carotene.
    Nutrients, 2025 · checked 2026-09-25
17. carpar-daily-r3-17 · meta-analysis of prospective studies
    Carrots are main dietary sources of several potential anti-cancer compounds, including polyacetylenes, while β-carotene has shown no benefits in controlled cancer trials.
    Crit Rev Food Sci Nutr, 2025 · checked 2026-09-25