Iodine and selenium intakes and status and thyroid function in midlife women with low bread intakes in New Zealand

Iodine and selenium are important nutrients for thyroid function; however, the New Zealand food supply is generally low in both minerals. Bread can be a good source of these minerals; although the popularity of lower carbohydrate diets means some people avoid bread. This study aimed to investigate the effect of low bread intakes on iodine and selenium intakes and status, and thyroid function in mid-life women in New Zealand.

Self-selecting women (n = 46), aged 40-63 years, with a mean daily intake of 1.6 ± 1.5 slices of fortified commercial bread, were recruited into a cross-sectional study in Auckland, New Zealand. Assessment of iodine and selenium intake was via a 3-day diet diary. Iodine and selenium concentrations were measured in 24-h urine samples and selenium concentrations in plasma using inductively coupled plasma mass spectrometry. Thyroid hormones including triiodothyronine and thyroxine were also determined.

Median urinary iodine concentration was 49 (35, 78; 25, 75 centile) μg/L indicating iodine deficiency. Of plasma samples measured, 32% had selenium concentrations below 110 μg/L, suggesting inadequacy. Data suggested at least 40% of participants had low intakes of both nutrients. Only two participants had impaired thyroid function; however, plasma selenium concentrations predicted the ratio of triiodothyronine to thyroxine (p = 0.038).

A high prevalence of inadequate selenium and iodine intake was observed in women with low bread intakes. Those with low bread intakes need to ensure they consume alternative sources such as dairy, fish and seafood, eggs, meat, other grains, and nuts.