Background
Mushrooms are a good source of many nutrients which are potentially beneficial for chronic diseases. We speculated that due to its abundant nutrients edible mushrooms might have a beneficial effect on the prevention of subclinical thyroid dysfunction (SCTD). Therefore, we designed a large-scale cohort study to examine whether mushrooms consumption is a protective factor for SCTD in adults.
Subclinical thyroid dysfunction (SCTD) is characterized by abnormal serum thyroid-stimulating hormone (TSH) levels and normal free thyroxine (FT4) and free triiodothyronine (FT3) levels [1]. Although only a small proportion of patients with SCTD have symptoms, the prevalence of SCTD is higher than overt thyroid disease , and the risk of progression of SCTD to overt thyroid disease is approximately 2 % to 6 % per year . SCTD can have repercussions on the cardiovascular system and bone, as well as on other organs and systems . Thus, prevention and treatment of SCTD has become an important public health concern. Moreover, though a number of synthetic drugs are available for managing this condition, their long-term use is associated with many side effects. Study showed levothyroxine therapy may be associated with iatrogenic thyrotoxicosis, especially in elderly patients, and there is no evidence that it is beneficial in persons aged 65 years or older . Therefore, this has shifted the research in SCTD towards medicinal plants and herbs which are considered to be comparatively safe.
Edible mushrooms have been widely used as health foods, because of their various bioactive constituents such as polysaccharides, proteins, vitamins, minerals, and dietary fiber . Mushrooms have the potential to be the only non-animal, unfortified food source of vitamin D that can provide a substantial amount of vitamin D2 in a single serve . There are two forms of vitamin D, vitamin D3 (or cholecalciferol) and vitamin D2 (or ergocalciferol). Both forms of vitamin D are transported to the liver where they are converted to 25-hydroxyvitamin D, which is the major circulating and stored form of vitamin D . Several clinical studies , have reported low vitamin D levels [(25(OH)D level] in people with autoimmune thyroid diseases, indicating an association between vitamin D deficiency and thyroid autoimmunity. Moreover, mushrooms flavonols can inhibit the activities of enzymes antithyroperoxidase and liver deiodinase as the key enzyme in the biosynthesis of thyroid hormones, bringing about changes in thyroid functions . Thus, we speculated that due to its abundant nutrients edible mushrooms might have a beneficial effect on the prevention of SCTD.
However, to date, the potential effects of habitual edible mushrooms consumption on SCTD have not been evaluated in population-based studies. Therefore, we conducted a large prospective cohort study to investigate whether edible mushrooms consumption were associated with SCTD in general adult population.
Methods
This prospective cohort study investigated 6631 participants (mean age: (45.0 ± 10.2) years; 55.1 % men). Edible mushrooms consumption was measured at baseline using a validated food frequency questionnaire. SCTD was defined as abnormal serum thyroid-stimulating hormone levels and normal free thyroxine. Cox proportional hazards regression models were used to examine the association of edible mushrooms consumption with incident SCTD.
Fig. 1. Flow diagram of study participant selection.
Results
During follow-up period, a total of 262 new cases of SCTD were identified, the incidence rate of subclinical hypothyroidism was 8.9/1000 person-years and subclinical hyperthyroidism was 7.2/1000 person-years. After adjusting potential confounding factors, the multivariable hazard ratios (95 % confidence intervals) for subclinical hypothyroidism were 1.00 (reference) for almost never, 0.53 (0.29, 0.97) for 1–3 times/week and 0.30 (0.10, 0.87) for ≥ 4 times/week (P for trend = 0.02). It also showed edible mushrooms consumption was inversely associated with subclinical hypothyroidism in obese individuals but not non-obese individuals, the final hazard ratios (95 % confidence intervals) were 0.14 (0.03, 0.73) (P for trend < 0.01).
Conclusions
his population-based prospective cohort study has firstly demonstrated that higher edible mushrooms consumption was significantly associated with lower incidence of subclinical hypothyroidism among general adult population, especially in obese individuals.
