# Do Cruciferous Vegetables Really Affect Your Thyroid?

**By Merve Tığlı** · 2026-10-01

Broccoli, cauliflower, cabbage and Brussels sprouts are at their absolute best in Victoria right now — sweet, tight-headed and cheap. And almost every winter, someone asks me the same worried question: "But I've read I shouldn't eat these if I have a thyroid problem." If that thought has ever made you put the broccoli back down, this one is for you.

### Where the worry came from

The concern has a real origin. Brassica vegetables — the cabbage family — contain sulfur compounds called **glucosinolates**. When the raw plant is chopped or chewed, an enzyme called myrosinase is released and breaks those compounds down into isothiocyanates and thiocyanates, some of which can compete with iodine uptake by the thyroid gland.

Historically, the clearest problems showed up in livestock grazing on raw or silage brassica crops, and in populations where these vegetables made up a very large share of the diet. Crucially, the effect was most pronounced in regions where the water and soil were also iodine-deficient.

### What the evidence actually shows in humans

A 2024 systematic review in the _International Journal of Molecular Sciences_ pooled 123 in vitro, animal and human studies on brassica vegetables and thyroid function. Its conclusion was reassuring: the great majority of the findings cast doubt on the assumption that brassica plants have antithyroid effects in humans, and instead indicate that including these vegetables in the daily diet — particularly alongside adequate iodine intake — poses no adverse effect on thyroid function.

Notice the condition attached to that sentence. It isn't "brassicas are fine, ignore everything." It's "brassicas are fine _when your iodine is adequate_." That's the part worth acting on.

### So the real question is your iodine, not your broccoli

In Australia the recommended dietary intake of iodine is 150 µg a day for adults, rising to 220 µg in pregnancy and 270 µg while breastfeeding. Since 2009, all commercial bread here (organic bread aside) has been made with iodised salt, and the Better Health Channel notes this means most of the Australian population now consumes enough — pregnant women being the exception. Seafood two to three times a week, eggs, dairy and iodised salt round it out. Australian soils are low in iodine, so home-grown vegetables contribute very little.

### Three practical things

**1\. Cook them, and the issue shrinks further.** Cooking deactivates myrosinase, so the compounds most often blamed aren't formed in the same way. Roasting, steaming and braising all count — which is convenient, because that's how most of us eat cabbage and cauliflower in winter anyway.

**2\. Keep raw amounts sensible.** The situations that have raised genuine concern involved very large, sustained intakes of raw brassicas — nothing like a shaved sprout slaw or a handful of raw kale in a salad. Normal portions are not the same thing.

**3\. Don't self-prescribe iodine.** Too much iodine can cause some of the same problems as too little, and it can be genuinely risky if you already have a thyroid condition. Iodine supplements are a conversation with your doctor, not a supermarket decision.

If you have Hashimoto's, an underactive or overactive thyroid, or you're pregnant, none of this replaces the plan you've made with your own doctor or dietitian. But for most people, the winter vegetables sitting in the fridge aren't the problem. They're fibre, folate, vitamin C and flavour, at their cheapest and best all year. Roast a tray of them this week.

_This is general information, not individual advice. If you have a diagnosed thyroid condition, are pregnant or breastfeeding, or take thyroid medication, please speak with your doctor or an Accredited Practising Dietitian before changing your diet or starting any supplement._

_Merve Tığlı, Dietitian_

_Sources: Paśko P, et al., "Do Brassica Vegetables Affect Thyroid Function? — A Comprehensive Systematic Review", International Journal of Molecular Sciences, 2024;25(7):3988; Better Health Channel (Victorian Department of Health), "Iodine"; Nutrient Reference Values for Australia and New Zealand, NHMRC._

**Tags:** healthy-cooking, nutrition, thyroid, wellness

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> Source: [nFit Diet & Nutrition](https://shop.nfitdiet.com/blogs/news/cruciferous-vegetables-thyroid)