Octopus: a modest portion with a very large vitamin B12 number

Selenium from seafood does reach the blood. In a 26-week trial in 102 healthy Danish adults aged 48 to 76, eating 35 oz (1,000 g) of fish and mussels a week raised whole blood selenium by 14.9 ng/mL against controls, with a 95% confidence interval of 10.2 to 19.7. Octopus was not on that menu, and the rise was smaller than the intake predicted. Octopus itself is known from food tables. USDA puts raw octopus at 20 mcg of vitamin B12 per 3.5 oz (100 g), 833% of the Daily Value, with 44.8 mcg of selenium and 0.435 mg of copper, from a single SR Legacy record. The UK table gives 75 mcg of selenium, 40% more, a gap that may reflect natural spread in seafood. An unspecified portion in the US dietary survey is 85 g, which works out at about 17 mcg of B12 from the raw figure.

The numbers, per 3.5 oz (100 g)

As people eat it, per 3.5 oz (100 g)

How much is actually in it

• USDA puts raw octopus at 20 mcg of vitamin B12 per 3.5 oz (100 g), which is 833% of the Daily Value, with 44.8 mcg of selenium and 0.435 mg of copper. — USDA SR Legacy record Mollusks, octopus, common, raw, FDC 174218 (n = 3 records) Evidence E source
  Vitamin B12 20 mcg (833% DV), selenium 44.8 mcg (81% DV), copper 0.435 mg (48% DV) per 3.5 oz (100 g) raw; B12 20 to 36 mcg and selenium 44.8 to 89.6 mcg across records including cooked
• The UK food table gives raw octopus 83 calories, 17.9 g protein and 1.3 g fat per 3.5 oz (100 g), and 75 mcg of selenium, which is 40% more than the USDA figure. — CoFID 2021 record 16-259 Octopus, raw (n = 1 record) Evidence E source
  Energy 83 calories, protein 17.9 g, fat 1.3 g, cholesterol 48 mg, selenium 75 mcg, iodine 20 mcg, zinc 1.7 mg, iron 1.2 mg, copper 0.40 mg per 3.5 oz (100 g); selenium 75 against USDA 44.8 mcg

What a real portion looks like

• The US dietary survey counts a cup of octopus as 135 g and an unspecified portion as 85 g, which carries about 17 mcg of vitamin B12 raw-equivalent. — FNDDS portion weights for Octopus (26205110) (n = 1 food) Evidence E source
  1 cup 135 g; quantity not specified 85 g; 85 g times 20 mcg per 3.5 oz (100 g) gives about 17 mcg vitamin B12

What your body absorbs

• In a 26-week trial in 102 Danish adults, 35 oz (1,000 g) of fish and mussels a week raised whole blood selenium by 14.9 ng/mL against controls. — 102 healthy non-smoking adults aged 48 to 76, Denmark, 26 weeks (n = 102) Evidence B source
  Whole blood selenium +14.9 ng/mL (95% CI 10.2 to 19.7); plasma selenoprotein P +7.0 ng/mL (3.1 to 10.9); smaller rise than expected from about 50 mcg selenium a day
• In a 4-week crossover trial in 20 Norwegian adults, a lean seafood diet raised median urinary iodine from 70 to 135 mcg/L, while the non-seafood diet did not. — 20 adults, mean age 50.6, two 4-week diets with 60% of protein from lean seafood or non-seafood (n = 20) Evidence B source
  Urinary iodine median 70 to 135 mcg/L on lean seafood against 79 to 58 mcg/L on non-seafood (P < 0.001); plasma selenium up (P = 0.001); urinary and plasma arsenic up (P < 0.001)

What cooking and storage change

• Simmering lean seafood keeps about 85% of its vitamin B12 in the USDA retention table, and all of its zinc, iron and copper. — USDA retention factors for the group Finfish and Shellfish Products, the group of octopus by its own USDA record Evidence E source
  FINFISH,<5%FAT,SIMMERED,WO/DRIPPING (Retn_Code 2401): vitamin B12 85%, niacin 85%, potassium 85%, thiamin 80%, zinc, iron and copper 100% retained; selenium absent from Release 6
• In 48 people with shellfish allergy, skin tests with raw and boiled octopus, squid and limpet extracts reacted alike, so cooking does not remove these allergens. — 48 patients with shellfish hypersensitivity, mean age 24, Spain (n = 48) Evidence C source
  No significant difference between raw and boiled extracts on prick testing; clinical association between cephalopods and bivalves (clam p < 0.05, mussel p < 0.01) but not with crustaceans

Safety, limits and interactions

• In 1,272 Danish 22-year-olds tested by oral challenge, octopus allergy was confirmed in 0.1%, the same share as cow's milk and codfish. — unselected cohort of 1,272 young adults aged 22, Denmark (n = 1272) Evidence C source
  Confirmed primary food hypersensitivity 1.7% (1.1 to 2.95); peanut 0.6%, additives 0.5%, shrimp 0.2%, codfish, cow's milk, octopus and soy 0.1% each
• In a 14-day trial in 38 healthy adults eating 5.3 oz (150 g) a day of cod, salmon or mussels, TSH rose in all seafood groups in step with blood arsenic. — 38 healthy volunteers randomized to cod, salmon, blue mussels or potato, 14 days (n = 38) Evidence B source
  Plasma TSH increased significantly in all seafood groups; change in plasma arsenic was the dominant predictor of TSH change (R2 = 0.47)
• In Italian market samples, cadmium exceeded the EU maximum level in squid, a close relative of octopus, while mercury stayed highest in predatory fish. — 12 fish and seafood products from the Italian market, including European and veined squid (n = 12 products) Evidence C source
  Cadmium above EU maximum levels in squid, red mullet, hake and cod; squid lead at 60% of the maximum level; median Italian consumer at 20% of the tolerable weekly cadmium intake from fish and seafood

What people believe that the data does not support

• In 18 men fed six kinds of shellfish, a squid diet, higher in cholesterol, did not change blood lipids and raised HDL2 cholesterol. — 18 normolipidemic men, controlled feeding with shellfish replacing other animal protein (n = 18) Evidence C source
  Squid and shrimp diets did not change blood lipids; oyster, mussel and squid diets increased HDL2 cholesterol

Who this works differently for

• Across 61 population studies, shellfish allergy confirmed by food challenge ranged from 0% to 0.9%, while self-report gave up to 10.3%. — 61 population-based cross-sectional and cohort studies worldwide (n = 61 studies) Evidence C source
  Shellfish allergy 0% to 10.3% depending on diagnosis; 0% to 0.9% where food challenges were used; possibly higher in Southeast Asia
• A forensic case series includes a death from choking on octopus tentacles in a man treated for depression, one of several food bolus deaths in people with impaired swallowing. — 4 fatal choking cases, one on octopus tentacles in a 38-year-old man (n = 1) Evidence D source
  Fatal airway obstruction by octopus tentacles
• A review of 46 studies on molluscs and crustaceans in pregnancy and early childhood found higher contaminant biomarkers, mainly mercury, and a benefit mostly for iodine status. — 46 studies of shellfish intake in pregnancy, lactation or children aged 0 to 2 (n = 46 studies) Evidence C source
  Shellfish intake associated with higher mercury biomarkers; associated with iodine status; no association with preterm birth; mixed results with some lower birth weight

The bottom line

Per 100 g the UK table gives raw octopus 83 calories, 17.9 g of protein and 1.3 g of fat. Simmering lean seafood keeps about 85% of vitamin B12 and all the zinc, iron and copper in the USDA group table, which is built on finfish. Octopus is usually cooked far longer, so real losses may be larger. In a 4-week crossover trial in 20 Norwegian adults, a lean seafood diet raised median urinary iodine from 70 to 135 mcg/L while a non-seafood diet did not, and urinary arsenic rose as well. That diet was mostly white fish. Squid, the nearest relative with feeding data, is higher in cholesterol. In 18 men on a controlled diet in a small study from 1990, squid did not change blood lipids and raised HDL2 cholesterol. Who should be careful. Octopus allergy exists and is uncommon. In 1,272 unselected Danish 22-year-olds tested by oral challenge, it was confirmed in 0.1%, a handful of people and an imprecise figure, the same share as cow's milk and cod. In skin tests on 48 Spanish patients with shellfish allergy, raw and boiled octopus, squid and limpet extracts reacted alike, so cooking did not reduce reactivity, and reactions to cephalopods went together with reactions to clams and mussels but not with crustaceans. Across 61 population studies, shellfish allergy confirmed by food challenge ranged from 0% to 0.9% against up to 10.3% by self-report, and those data are mostly about crustaceans. In a 14-day trial in 38 healthy adults eating 5.3 oz (150 g) a day of cod, salmon or mussels, TSH rose in every seafood group in step with blood arsenic. Cephalopods were not tested, and what a TSH rise within the normal range means is unknown. In a pilot sample from Italian markets, squid exceeded the EU cadmium limit. For pregnancy and children under 2, a review of 46 mostly observational studies linked shellfish with higher mercury markers and with iodine status, without pooled numbers. One forensic case describes a 38-year-old man in treatment for depression who choked to death on octopus tentacles, a firm, rubbery food that is a risk for people whose swallowing is impaired.

Compared with other foods

Sources

1. octo-r8-01 · USDA FoodData Central SR Legacy, dataset
   Mollusks, octopus, common, raw (FDC 174218, SR Legacy, Finfish and Shellfish Products): vitamin B12 20 mcg per 100 g = 833% DV; selenium 44.8 mcg = 81% DV; copper 0.435 mg = 48% DV; range over records B12 20-36, selenium 44.8-89.6, copper 0.37-0.739; Foundation samples 0
   USDA FoodData Central, SR Legacy, FDC 174218 · checked 2026-09-29
2. octo-r8-02 · CoFID 2021, dataset
   CoFID 16-259 Octopus, raw: Energy 83 kcal, Protein 17.9 g, Fat 1.3 g, Cholesterol 48.0 mg, Selenium 75 µg, Iodine 20 µg, Zinc 1.7 mg, Iron 1.20 mg, Copper 0.40 mg per 100 g
   CoFID 2021, Public Health England, code 16-259 · checked 2026-09-29
3. octo-r8-03 · USDA FNDDS, dataset
   Octopus (FNDDS 26205110, fdc_id 2706331, WWEIA Shellfish): 1 cup 135 g; Quantity not specified 85 g
   USDA FNDDS, fdc_id 2706331 · checked 2026-09-29
4. octo-r8-09 · randomized controlled trial
   The difference in mean change for intervention compared with control persons was 14.9 ng/mL (95% CI: 10.2, 19.7) for whole blood selenium, and 7.0 ng/mL (95% CI: 3.1, 10.9) for plasma SelP (Weeks 0-26).
   Nutrients, 2015 · checked 2026-09-29
5. octo-r8-10 · randomized crossover trial
   UIC increased after 4 weeks of the lean-seafood intervention to 135 (110, 278) µg/L, but not after the non-seafood intervention [58 (33, 91) µg/L] (P diet-effect < 0.001).
   Eur J Nutr, 2021 · checked 2026-09-29
6. octo-r8-04 · USDA Table of Nutrient Retention Factors, dataset
   USDA-RETN-R6:2401 FINFISH,<5%FAT,SIMMERED,WO/DRIPPING, group Finfish and Shellfish Products: vitamin_b12_ug 85% retained, niacin_mg 85%, potassium_mg 85%, thiamin_mg 80%, zinc_mg 100%, iron_mg 100%, copper_mg 100%; selenium not in Release 6
   USDA Table of Nutrient Retention Factors, Release 6, 2007, Retn_Code 2401 · checked 2026-09-29
7. octo-r8-05 · clinical series
   Significant differences among prick-tests with raw and boiled extracts were not found.
   Allergol Immunopathol (Madr), 1994 · checked 2026-09-29
8. octo-r8-06 · cohort
   In primary FHS, the most common allergenic food was peanut (0.6%) followed by additives (0.5%), shrimp (0.2%), codfish (0.1%), cow's milk (0.1%), octopus (0.1%) and soy (0.1%).
   Pediatr Allergy Immunol, 2009 · checked 2026-09-29
9. octo-r8-11 · randomized controlled trial
   Ingestion of seafood rich in various organic As species was strongly associated with an increase of the TSH concentrations in plasma.
   J Trace Elem Med Biol, 2017 · checked 2026-09-29
10. octo-r8-12 · exposure assessment
    This metal exceeded the MLs in squid, red mullet, European hake and Atlantic cod.
    Food Addit Contam Part A Chem Anal Control Expo Risk Assess, 2012 · checked 2026-09-29
11. octo-r8-13 · controlled feeding trial
    Squid and shrimp diets, higher in cholesterol and lower in n-3 fatty acids, did not change the blood lipids.
    Am J Clin Nutr, 1990 · checked 2026-09-29
12. octo-r8-07 · systematic review
    Where food challenges were used, the prevalence for fish allergy was found to be 0% to 0.3% and for shellfish allergy was 0% to 0.9%.
    Ann Allergy Asthma Immunol, 2016 · checked 2026-09-29
13. octo-r8-08 · case series
    a 38-year-old subject in psychiatric treatment for depressive disorder who died from clogging with octopus tentacles
    Clin Ter, 2024 · checked 2026-09-29
14. octo-r8-14 · scoping review
    Overall, shellfish consumption was associated with higher biomarkers of environmental contaminants, with mercury being the most studied and having the strongest evidence base.
    Nutr Res Rev, 2025 · checked 2026-09-29