What to Combine Iodine With
Iodine rarely gets attention in sports nutrition, yet it is essential for producing thyroid hormones, which regulate metabolic rate, growth and energy use. The UK has no mandatory salt iodisation, and surveys have repeatedly found mild deficiency in some groups. Our editorial team looked at which nutrients support iodine's role, which combinations to avoid, and when supplements make sense.
Why iodine matters and how much we need
The thyroid gland uses iodine to make thyroxine (T4) and triiodothyronine (T3). These hormones influence almost every tissue, from muscle and heart to the brain. Without enough iodine, the thyroid cannot keep up with demand and may enlarge, forming a goitre, while hormone levels can fall.
In the UK, the reference nutrient intake for adults is 140 micrograms per day. The World Health Organization recommends 250 micrograms daily during pregnancy and breastfeeding, reflecting the importance of iodine for foetal brain development.
The main dietary sources in Britain are milk and dairy products, fish and seafood, and eggs. Iodine in milk is largely a consequence of iodine added to cattle feed. People who avoid dairy and fish, including many vegans and those drinking plant-based milks without added iodine, are at greater risk of low intake.
A survey of UK schoolgirls by Vanderpump and colleagues, published in The Lancet in 2011, found mild iodine deficiency in a substantial proportion of participants. A later analysis of the ALSPAC cohort by Bath and colleagues linked inadequate iodine status in pregnancy with lower verbal IQ and reading scores in children.
Selenium: iodine's most important partner
Selenium is the nutrient most closely connected with iodine. The enzymes that convert T4 into the more active T3, called deiodinases, contain selenium. Glutathione peroxidases, which protect the thyroid from the hydrogen peroxide generated during hormone production, also depend on selenium.
When both iodine and selenium are low, thyroid function may be more impaired than with either deficiency alone. A review by Zimmermann and Köhrle in Thyroid described how combined deficiencies influence thyroid metabolism. Equally, correcting iodine in someone who is severely selenium deficient may theoretically stress the thyroid, which is why balanced intake matters.
UK soils are relatively low in selenium, and intakes in Britain fell when imports of selenium-rich North American wheat declined. Good sources include Brazil nuts, fish, eggs and offal. Just one or two Brazil nuts can provide a substantial amount, although selenium content varies widely between nuts.
Selenium also has a narrow safe range. Long-term excessive intake can cause selenosis, with hair and nail loss and digestive symptoms. A combined multivitamin with moderate amounts of both nutrients is generally safer than high-dose single supplements.
| Nutrient | Role related to iodine | Main UK food sources |
|---|---|---|
| Selenium | Activates thyroid hormones; protects the gland | Brazil nuts, fish, eggs |
| Iron | Needed by thyroid peroxidase enzyme | Red meat, pulses, fortified cereals |
| Zinc | Supports thyroid hormone metabolism | Meat, shellfish, seeds |
| Vitamin A | Influences thyroid hormone signalling | Dairy, eggs, orange vegetables |
Iron, zinc and vitamin A
Thyroid peroxidase, the enzyme that attaches iodine to the protein backbone of thyroid hormones, contains haem iron. Iron deficiency anaemia can therefore reduce the efficiency of iodine use. This is especially relevant for menstruating women and endurance athletes, both groups with higher rates of low iron status.
Studies in regions with combined deficiencies have shown that iodine supplementation works less well in children who are also iron deficient, and that correcting iron improves the response. In the UK the relevance is mostly for individuals with diagnosed iron deficiency rather than the general population.
Zinc and vitamin A also influence thyroid hormone metabolism and signalling, although their effects are less direct. A varied diet normally supplies enough of both, and there is little reason for most people to supplement them specifically to support iodine.
Combinations to avoid or approach carefully
Some pairings with iodine call for caution, either because they push intake too high or because of interactions with medicines:
We often recommend Sp Turabolan 10 mg.
- Kelp and seaweed supplements. Iodine content varies hugely and can far exceed safe limits. Combining these with an iodine-containing multivitamin increases the risk of excess.
- Thyroid medication. People taking levothyroxine or antithyroid drugs should not add iodine supplements without medical advice.
- Amiodarone and lithium. Amiodarone contains a large amount of iodine, and lithium affects thyroid function; extra iodine can complicate treatment.
- Potassium-sparing drugs. Potassium iodide supplements add potassium, which matters for people on certain blood pressure or heart medicines.
- Multiple overlapping products. Many pre-workouts, greens powders and "metabolism" blends include iodine; add up the total.
The tolerable upper intake level set by the European Food Safety Authority for adults is 600 micrograms per day. Both too little and too much iodine can disturb thyroid function, sometimes causing an overactive or underactive thyroid in susceptible people, particularly those with existing thyroid disease.
Goitrogens in foods such as raw cruciferous vegetables and soy are sometimes mentioned as iodine antagonists. In practice, normal amounts in a varied diet are not a concern for people with adequate iodine intake.
Who might consider an iodine supplement
Most people who regularly consume milk, yoghurt, fish and eggs meet their iodine needs from food. Supplements become worth considering for those who avoid these foods entirely, such as vegans, or who rely on unfortified plant milks.
The NHS advises that if you do not eat fish or dairy, you may want to consider an iodine supplement, and to choose one based on potassium iodide or potassium iodate rather than seaweed. Women planning pregnancy, pregnant or breastfeeding should discuss iodine with their midwife or GP.
For athletes, there is no evidence that extra iodine above requirements improves performance or fat loss. Claims that iodine "boosts metabolism" apply only to correcting deficiency, not to adding more in someone already replete.
A sensible approach for those who need it is a multivitamin or a standalone supplement providing around the reference intake, rather than high-dose products.
Conclusions of the editorial team
Iodine works as part of a team. Selenium is its closest partner, and iron, zinc and vitamin A also support thyroid function. Ensuring adequate intake of all of these through diet is more useful than high doses of any one.
The main risks come from excess, especially through kelp supplements, overlapping products and interactions with thyroid or heart medication. People who avoid dairy and fish are the main group who may benefit from a modest iodine supplement.
For further reading, we suggest our articles on selenium and the thyroid, on iron status in endurance athletes, and on nutrient gaps in vegan diets.
References
- Zimmermann MB, Boelaert K. Iodine deficiency and thyroid disorders. Lancet Diabetes Endocrinol. 2015;3(4):286–295.
- Zimmermann MB, Köhrle J. The impact of iron and selenium deficiencies on iodine and thyroid metabolism: biochemistry and relevance to public health. Thyroid. 2002;12(10):867–878.
- Vanderpump MP, Lazarus JH, Smyth PP, et al. Iodine status of UK schoolgirls: a cross-sectional survey. Lancet. 2011;377(9782):2007–2012.
- Bath SC, Steer CD, Golding J, Emmett P, Rayman MP. Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet. 2013;382(9889):331–337.
- Rayman MP. Selenium and human health. Lancet. 2012;379(9822):1256–1268.
