# Brassica oleracea var. sabellica (Curly Kale)

**Canonical URL:** https://ingredients.hermeticasuperfoods.com/ingredients/brassica-oleracea-var-sabellica
**Data Source:** Hermetica Superfoods Ingredient Encyclopedia
**Updated:** 2026-03-24
**Evidence Score:** 2 / 10
**Category:** Vegetable
**Also Known As:** Brassica oleracea var. sabellica, Curly kale, Scotch kale, Winter kale, Boerenkool, Chou frisé, Grünkohl, Kale

## Overview

Curly kale (Brassica oleracea var. sabellica) contains high concentrations of carotenoids like β-carotene and lutein that support [antioxidant activity](/ingredients/condition/antioxidant) and eye health. Biofortified varieties demonstrate enhanced iodine bioavailability through compounds like 5,7-diiodo-8-quinolinol.

## Health Benefits

• Enhanced iodine bioavailability when biofortified - rat studies show higher absorption from 5,7-diiodo-8-quinolinol-enriched kale vs standard diets (preliminary evidence)
• Rich source of carotenoids including β-carotene and lutein - naturally occurring in all varieties (observational data)
• High dietary fiber content from pectin - increases with steaming in 'Oldenbor F₁' and 'Redbor F₁' varieties (in vitro evidence)
• Contains glucosinolates - characteristic bioactive compounds of cruciferous vegetables (compositional analysis)
• Low sugar content - glucose ~2x less, fructose ~4-5x less than cauliflower/cabbage (comparative analysis)

## Mechanism of Action

β-carotene undergoes cleavage by β-carotene 15,15'-oxygenase to form retinal, supporting vitamin A [metabolism](/ingredients/condition/weight-management). Lutein accumulates in macular tissue through xanthophyll-binding proteins, filtering blue light and reducing [oxidative stress](/ingredients/condition/antioxidant). Biofortified kale delivers iodine via organically-bound compounds like 5,7-diiodo-8-quinolinol, which may improve [thyroid](/ingredients/condition/hormonal) hormone synthesis.

## Clinical Summary

Rat studies demonstrate superior iodine absorption from biofortified kale containing 5,7-diiodo-8-quinolinol compared to standard diets, though human trials are lacking. Observational studies confirm curly kale as a significant source of carotenoids, with varieties containing 3-15 mg/100g β-carotene. No randomized controlled trials have specifically tested curly kale supplementation for health outcomes. Evidence remains preliminary and largely observational.

## Nutritional Profile

Curly kale (Brassica oleracea var. sabellica) is a nutrient-dense leafy green with the following approximate composition per 100g raw weight: Macronutrients: energy ~49 kcal, carbohydrates ~8.8g, dietary fiber ~3.6g (predominantly pectin, which increases upon steaming particularly in 'Oldenbor F₁' and 'Redbor F₁' cultivars), protein ~4.3g (relatively high for a leafy vegetable, containing all essential amino acids though lysine is limiting), fat ~0.9g. Key vitamins: vitamin K1 (phylloquinone) ~704µg (588% DV - highest among common vegetables), vitamin C ~120mg (133% DV, though significantly reduced by cooking ~50-60%), vitamin A (as β-carotene) ~681µg RAE, folate ~141µg, vitamin B6 ~0.27mg, vitamin E (α-tocopherol) ~1.54mg. Key minerals: calcium ~150mg (bioavailability ~49-60%, notably higher than spinach due to lower oxalate content), potassium ~491mg, magnesium ~47mg, phosphorus ~92mg, manganese ~0.66mg, iodine (variable, typically 5-10µg/100g in standard cultivation, significantly elevated in biofortified varieties). Bioactive compounds: glucosinolates ~100-150mg/100g fresh weight (predominantly gluconapin, sinigrin, and glucobrassicin - hydrolyzed to isothiocyanates including sulforaphane upon chewing or cooking), carotenoids including β-carotene (~9990µg), lutein+zeaxanthin (~39.55mg per 100g - among the richest dietary sources), quercetin and kaempferol flavonoids (~34mg combined), chlorophyll (~1500mg/kg dry weight). Bioavailability notes: fat-soluble carotenoids (lutein, β-carotene) absorption increases 3-5x when consumed with dietary fat; steaming preserves glucosinolates better than boiling (which leaches ~40% into cooking water); oxalate content (~20mg/100g) is low relative to spinach, supporting better calcium and mineral absorption; vitamin C and folate are heat-labile and best preserved in raw or lightly steamed preparations.

## Dosage & Preparation

No clinically studied dosage ranges have been established for curly kale as human trials are lacking. Agronomic studies modeled daily intake at 0.1 kg fresh weight, with biofortified varieties reaching up to 2434.70 μg/kg dry weight iodine content. Consult a healthcare provider before starting any new supplement.

## Safety & Drug Interactions

Curly kale contains goitrogens that may interfere with [thyroid function](/ingredients/condition/hormonal) when consumed in large quantities, particularly in iodine-deficient individuals. High vitamin K content may interact with warfarin and other anticoagulant medications. Generally recognized as safe when consumed as food, though supplement safety during pregnancy and lactation lacks specific research. Oxalate content may contribute to kidney stone formation in susceptible individuals.

## Scientific Research

No human clinical trials, RCTs, or meta-analyses on curly kale were identified in available research. The only in vivo study was a rat feeding experiment using Wistar rats fed biofortified kale varieties, demonstrating higher iodine bioavailability compared to standard diets (PMID: 38004124).

## Historical & Cultural Context

No historical or traditional medicine uses of curly kale (Brassica oleracea var. sabellica) are documented in the available research sources.

## Synergistic Combinations

Other cruciferous vegetables, vitamin D, selenium, zinc, vitamin A

## Frequently Asked Questions

### How much beta-carotene is in curly kale?

Curly kale contains approximately 3-15 mg of β-carotene per 100g fresh weight, varying by cultivar and growing conditions. This represents roughly 500-2500% of daily vitamin A needs when converted to retinal.

### Can curly kale affect thyroid function?

Yes, curly kale contains goitrogens that may interfere with iodine uptake by the thyroid gland. However, biofortified varieties may actually support thyroid function through enhanced iodine bioavailability from organically-bound compounds.

### What makes biofortified kale different from regular kale?

Biofortified kale is enriched with minerals like iodine through specialized growing techniques or soil amendments. Rat studies show compounds like 5,7-diiodo-8-quinolinol in biofortified kale provide better iodine absorption than standard inorganic iodine sources.

### How much lutein does curly kale provide?

Curly kale typically contains 18-47 mg of lutein per 100g fresh weight, making it one of the richest dietary sources. This amount significantly exceeds the 6-10 mg daily intake associated with eye health benefits in epidemiological studies.

### Does cooking affect curly kale's nutritional value?

Light cooking may actually increase carotenoid bioavailability by breaking down cell walls, though it can reduce water-soluble vitamins. Steaming preserves more nutrients than boiling, while excessive heat may degrade heat-sensitive compounds.

### What is the difference between raw and steamed curly kale for fiber intake?

Steaming curly kale varieties like 'Oldenbor F₁' and 'Redbor F₁' increases their pectin-based dietary fiber content compared to raw preparation. This thermal processing makes the fiber more accessible and can enhance overall digestive benefits, though the exact magnitude of increase varies by cultivar and steaming duration.

### Does biofortified kale with enhanced iodine absorb better than regular kale?

Preliminary rat studies suggest that biofortified kale enriched with 5,7-diiodo-8-quinolinol shows superior iodine bioavailability compared to standard kale varieties and conventional dietary iodine sources. However, human clinical evidence is limited, so these findings should be considered preliminary until confirmed in controlled human trials.

### Who should prioritize curly kale consumption for carotenoid and lutein intake?

Individuals with increased antioxidant needs—including those with age-related eye health concerns or limited fruit and vegetable intake—benefit most from curly kale's naturally high carotenoid and lutein content. Athletes and those with higher oxidative stress from intense physical activity may also see particular value from this nutrient-dense cruciferous vegetable.

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