Beetroot and carrot juice increase the risk of thyroid nodules and hypothyroidism in breast cancer patients

Abstract

After diagnosis, many breast cancer patients start consuming high quantities of beetroot and carrot juice, in the hope of improving the outcome of their treatment. However, these foods are very high in nitrate, which can competitively inhibit the uptake of iodine by the thyroid, potentially leading to hypothyroidism or thyroid nodules. We applied a nitrate and iodine food frequency questionnare (asking about dairy, fish, seafood and iodized salt for iodine intake and spinach, carrots, beetroot, lettuce and arugula for nitrate intake) to 353 ER+/PR±/HER2-luminal A and B breast cancer patients during antiestrogenic treatment. We excluded patients with a thyroid disease diagnosis prior to the cancer diagnosis, smokers, ex-smokers and those with renal disease or bipolar disorder. The only correlations found between dietary intake of iodine and nitrate and the incidence of de novo thyroid nodules were: decreased risk for a daily intake of minimum 250ml dairy; and increased risk for daily intakes of over 200g spinach, 250g carrots or 250g beetroot. The correlations between dietary intake of nitrate and the incidence of de novo hypothyroidism were: decreased risk for a daily intake of iodized salt 2.5g and minimum of 100g fish or 250ml dairy; and increased risk for daily intakes of over 250g carrots or 250g beetroot. The results of this study support the hypothesis that the increased intake of nitrate-rich foods – particularly beetroot and carrot juice – is a risk factor for de novo hypothyroidism or thyroid nodules, after a breast cancer diagnosis.

Keywords

• breast cancer
• thyroid disease
• beetroot juice
• competitive iodine inhibition by nitrate
• na+/i- symporter