Adherence to a Mediterranean Diet and Thyroid Function in Obesity: A Cross-Sectional Apulian Survey

Association Between Dietary Phytochemical Index and Neonatal Thyroid Function

Background: Thyroid hormones regulate fetal growth and differentiation of several tissues. Maternal dietary patterns may be correlated with changes in the level of neonatal thyroid-stimulating hormone (TSH). We hypothesized that since maternal nutrition affects birth weight and offspring growth, it may also impact endocrine patterns in offspring. This study is aimed at assessing the relationship between maternal dietary phytochemical index (DPI) in the first trimester of pregnancy and neonatal cord blood thyroid hormone levels. Methods: This cross-sectional study is a substudy of a birth cohort. Overall, 216 mothers, aged 16-45 years, were recruited in their first trimester of pregnancy. To calculate DPI, the daily energy percentage of phytochemical-rich foods was divided by the total daily energy intake. At delivery time, TSH and free thyroxine (FT4) levels were measured in cord blood samples using chemiluminescence immunoassay. Results: The mean (standard deviation (SD)) age of mothers was 29.56 (5.50) years, and 47% of newborns were girls. The mean (SD) of DPI in the first, second, third, and fourth quartiles was 25.03 ± 4.67, 33.87 ± 2.18, 40.64 ± 2.10, and 51.17 ± 4.98, respectively. There was not any significant correlation between DPI score with cord serum TSH and FT4 levels in crude and adjusted analysis. Conclusion: No significant relationship between maternal DPI with cord serum TSH and FT4 levels was shown. Limited experience exists about the effect of maternal diet quality indices on neonatal thyroid function, and further studies are needed in this regard.

The Effect of Mediterranean Diet on Thyroid Gland Activity

The main goal of this research was to determine whether there is a correlation between adherence to the Mediterranean diet (assessed by the Mediterranean Diet Serving Score (MDSS)) and parameters indicating thyroid gland activity, such as concentration of thyroid-stimulating hormone (TSH), thyroid hormones (free triiodothyronine (fT3), free thyroxine (fT4)), thyroglobulin (Tg), antibodies to thyroid proteins (thyroglobulin antibodies (TgAb) and thyroid peroxidase antibodies (TPOAb)), and calcitonin (CT) in plasma and serum samples. An additional objective was to investigate whether there are differences in the values of the MDSS among clinical groups (euthyroid individuals, euthyroid individuals with positive TgAb and/or TPOAb, and hypothyroid and hyperthyroid participants). This cross-sectional study included 4620 participants over 18 years of age from the islands of Korčula and Vis, and the mainland city of Split. The MDSS was assessed from a food frequency questionnaire (FFQ). MDSS values were significantly higher in females compared to males and showed a positive association with the age of the participants. There was no significant difference in the MDSS values among the examined clinical groups. In the group of subjects with euthyroidism, a significant positive association was found between fT3 and the MDSS, while in the group of subjects with subclinical hypothyroidism, a significant positive association was observed between the MDSS and both fT3 and fT4. CT levels were also positively associated with the MDSS. Considering the significant positive association of the MDSS and both fT3 and fT4 levels in patients with subclinical hypothyroidism, the results of this study could be used to create guidelines for selecting an appropriate, potentially protective diet for these patients.

Evaluation of the effect of gluten-free diet and Mediterranean diet on autoimmune system in patients with Hashimoto's thyroiditis

Hashimoto's thyroiditis is an autoimmune disease in which thyroid cells are attacked through cell-and antibody-mediated immune processes. A gluten-free diet reduces antibody concentration and regulates thyroid autoimmunization. Mediterranean diet reduces oxidative stress. This study evaluates the short-term effects of Mediterranean, gluten-free, and Mediterranean gluten-free dietary patterns on thyroid function and autoantibody levels of patients. The 40 patients with Hashimoto's thyroiditis included in the study were randomly divided into four groups (defined as gluten-free, Mediterranean, Mediterranean gluten-free, and controls) for 12 weeks. Thyroid function tests, autoantibody levels, and food consumption were recorded at the beginning and end of the study. There was no statistically significant difference in TSH levels of the groups before the intervention, but a statistically significant difference was found afterward (p < 0.05). Free T3 hormone levels showed a statistically significant difference across the groups before and after the intervention (p < 0.05). Free T3 hormone levels increased significantly in all intervention groups after the intervention, with the highest increase in the Mediterranean group (p < 0.05). In the intervention groups, anti-TPO and anti-Tg levels decreased after the intervention; however, this difference was not significant across groups (p > 0.05). In addition, body weight, body mass index, waist and hip circumference averages decreased significantly in all intervention groups compared with controls (p < 0.05). The study achieved an increase in Free T3 hormone levels in the intervention groups. The most marked difference was seen in the Mediterranean gluten-free diet model, which may be due to the anti-inflammatory effect of both Mediterranean and gluten-free diets and the loss of body weight as a result of the intervention.

Dietary Patterns and Hypothyroidism in U.S. Adult Population

The thyroid gland produces hormones that are essential for various body functions. Hypothyroidism is defined as insufficient thyroid hormone production. Several studies have found associations between specific micronutrients and overall thyroid function; however, the amount of evidence regarding the relationship between dietary patterns and hypothyroidism among the U.S. population is limited. Data from three cycles of National Health and Nutrition Examination Surveys (NHANES), 2007-2008, 2009-2010, and 2011-2012, were used (n = 8317). Subjects with serum thyroid stimulating hormone >4.5 mIU/L or on levothyroxine were considered to have hypothyroidism. Age, sex, race/ethnicity, body mass index, and several lifestyle factors were considered as covariates. Three patterns were extracted using factor analysis. These were labeled as fat-processed grains-sugars-meats (FPSM), oils-nuts-potatoes-low-fat meats (ONPL), and fruits-whole grains-vegetables-dairy (FWVD) patterns. In a weighted multiple logistic regression, FPSM and ONPL were inversely associated with hypothyroidism (OR, 0.75; 95% CI, 0.57-1; p = 0.049 and OR, 0.81; 95% CI, 0.67-0.97; p = 0.025, respectively). However, FWVD demonstrated no association with hypothyroidism (p = 0.63). In conclusion, FPSM and ONPL patterns but not FWVD patterns were associated with hypothyroidism in U.S. adults. Nutrient deficiencies and their interactions may be linked to hypothyroidism.

Correlation between systemic inflammatory response index and thyroid function: 2009-2012 NHANES results

Aims

This study investigates the relationship between the Systemic Inflammatory Response Index (SIRI) and thyroid function.

Methods

Utilizing data from the National Health and Nutrition Examination Survey (NHANES) 2009-2012, we excluded participants lacking SIRI or thyroid function data, those under 20 years, and pregnant individuals. SIRI was determined using blood samples. We conducted weighted multivariate regression and subgroup analyses to discern the independent relationship between SIRI and thyroid function.

Results

The study included 1,641 subjects, with an average age of 47.26±16.77 years, including 48.65% males and 51.35% females. The population was divided into three SIRI-based groups (Q1-Q3). Q3, compared to Q1, exhibited higher age-at-onset, greater male prevalence, and increased levels of FT3, FT4, TT4, leukocytes, and triglycerides. This group also showed a higher incidence of diabetes, hypertension, and smoking. Notably, Q1 had lower LDL and HDL levels. SIRI maintained a positive association with FT4 (β = 0.01, 95% CI = 0.00-0.03, P for trend = 0.0071), TT4 (β = 0.20, 95% CI = 0.10, 0.31, P for trend=0.0001), and TPOAb (β = 8.0, 95% CI = 1.77-14.30, P for trend = 0.0120), indicating that each quartile increase in SIRI corresponded to a 0.01 ng/dL increase in FT4, a 0.2 g/dL increase in TT4, and an 8.03 IU/mL rise in TPOAb. The subgroup analysis suggested the SIRI-thyroid function correlation was influenced by hypertension.

Conclusion

Inflammation may impact the development and progression of thyroid function disorders. Proactive anti-inflammatory treatment might mitigate thyroid abnormalities.

Cardiometabolic-related dietary patterns and thyroid function: a population-based cross-sectional study

BACKGROUND

Little is known about the association of dietary patterns with thyroid function. Since thyroid function and cardiometabolic variables are inter-related, we investigated whether cardiometabolic-related dietary patterns are associated with thyroid function.

METHODS

This cross-sectional study included 3520 Tehran Lipid and Glucose Study participants. Reduced rank regression was used to find dietary patterns with body mass index, serum fasting glucose, triglycerides, HDL-C, and systolic and diastolic blood pressures as response variables. Two patterns were retained, one based on 35 food groups (native-based pattern) and the other based on the European Prospective Investigation into Cancer and Nutrition Germany (EPIC) food grouping (n = 33). A confirmatory cardio-metabolic dietary pattern was also created according to the weight of food groups proposed by the Framingham Offspring Study (FOS). The association of each pattern with thyroid-stimulating hormone (TSH), free thyroxine, and thyroid peroxidase antibody (TPOAb) and the odds of thyroid dysfunction was examined by linear and logistic regression, respectively.

RESULTS

The two exploratory dietary patterns were highly correlated and associated with greater TSH levels in euthyroid participants. The adjusted odds ratio (95% CI) of subclinical hypothyroidism per one standard deviation was 1.14 (1.01, 1.28) for the native-based pattern and 1.16 (1.03, 1.31) for the EPIC-based pattern. The odds of subclinical hypothyroidism was significantly greater in the second and third tertiles of the native-based pattern compared to the first tertile in the adjusted model (p-trend = 0.005). The odds of subclinical hypothyroidism increased across the tertiles of the EPIC-based pattern, but the odds was significantly higher only in tertile 3 compared to tertile 1, with an OR (95% CI) of 1.44 (1.07, 1.94) in the adjusted model. The adjusted odds of clinical hypothyroidism were greater in tertile 3 of the native-based pattern compared with tertile 1 (OR = 1.65, 95% CI 1.04, 2.62). The patterns were unrelated to hyperthyroidism or TPOAb positivity. The FOS-based confirmatory score was unrelated to thyroid function.

CONCLUSIONS

A diet high in fast foods, soft drinks, and legumes and low in confectionery, potatoes, butter, and jam and honey was associated with higher TSH levels in euthyroidism and higher odds of subclinical hypothyroidism.

Relationship between thyroid function and dietary inflammatory index in Hashimoto thyroiditis patients

Inflammation is closely related to the changes of thyroid function in Hashimoto thyroiditis patients. Certain nutrients or dietary habits can alter the levels of autoantibodies in Hashimoto thyroiditis. However, it remains unclear whether dietary inflammation affects thyroid function in patients with Hashimoto thyroiditis. The purpose of this study was to assess the relationship between dietary inflammation and thyroid function in Hashimoto thyroiditis patients using data from the National Health and Nutrition Examination Survey. We employed weighted multivariable linear regression, subgroup analyses, and interaction analysis to explore the relationship between thyroid function and dietary inflammatory index. We found that dietary inflammatory index was positively correlated with TSH and total T4. Interaction analysis found an interaction between urinary iodine concentration and FT3, but subgroup analysis for different levels of urinary iodine concentration did not get statistically significant results. Hashimoto thyroiditis patients with more pro-inflammatory diet habits had higher levels of TSH and TT4. In order to prevent hypothyroidism more effectively in patients with Hashimoto thyroiditis, it is essential to control dietary inflammation. However, it is still necessary to design a better prospective cohort study to verify the causal relationship.

Autoimmune Thyroid Disorders: The Mediterranean Diet as a Protective Choice

Autoimmune thyroid diseases are on the rise worldwide, and such a rapid increase is mainly driven by environmental factors related to changed lifestyles in "modern" societies. In this context, diet seems to play a crucial role. An unhealthy high-energy diet, rich in animal fat and proteins, salt and refined sugars (the so-called "Western diet") negatively influences the risk of autoimmunity by altering the immune balance and the gut microbiota composition, enhancing oxidative stress and promoting inflammation. In contrast, the Mediterranean diet represents a unique model of healthy eating, characterized by a high intake of food from vegetable sources, a low consumption of saturated fats in favor of unsaturated fats (mainly, olive oil), a moderate consumption of fish (typically, the small oily fishes) and dairy products, as well as a moderate consumption of wine at meals, and a low intake of meat. Thanks to its nutritional components, the Mediterranean Diet positively influences immune system function, gut microbiota composition, and redox homeostasis, exerting anti-oxidants, anti-inflammatory, and immunomodulatory effects. The present review was aimed at exploring the existing knowledge on the correlations between dietary habits and thyroid autoimmunity, to evaluate the role of the Mediterranean diet as a protective model.

Higher Sensitivity to Thyroid Hormones May Be Linked to Maintaining the Healthy Metabolic Condition in People with Obesity: New Insight from NHANES

INTRODUCTION

Obesity contributes to the pathogenesis of diverse metabolic diseases, yet the mechanism underlying metabolically healthy obesity (MHO) remains elusive. Thyroid hormones and sensitivity to them have a major impact on metabolism. Our study aimed to investigate the association between MHO and thyroid hormone sensitivity.

METHODS

Thyroid hormone indices, including the thyroid-stimulating hormone (TSH) index (TSHI), the Thyrotroph Thyroxine Sensitivity Index (TTSI), the Thyroid Feedback Quantile-Based Index (TFQI), and the Parametric Thyroid Feedback Quantile-Based Index (PTFQI), were calculated based on a non-institutionalized US sample in the National Health and Nutrition Examination Survey (NHANES, 2007-2012). Participants were divided into four groups (metabolically healthy non-obesity [MHNO], metabolically unhealthy non-obesity [MUNO], MHO, and metabolically unhealthy obesity [MUO]) according to their body mass index and metabolic profiles. Linear regression, logistic regression, and restricted cubic splines were employed to analyze the association between thyroid hormone indices and metabolic phenotypes.

RESULTS

A total of 4,857 participants (49.6% men; mean age, 42.6 years) were included, with 1,539 having obesity and 235 identified as MHO. Participants in the MHO group exhibited lower levels of TSH, TSHI, TTSI, TFQI, and PTFQI compared with the MHNO group (all p < 0.05), while the differences among MHNO, MUNO, and MUO groups were not statistically significant (all p > 0.05). Among participants with obesity, TSH, TSHI, TTSI, TFQI, and PTFQI were positively associated with metabolic abnormality (all p < 0.05).

CONCLUSION

Participants with MHO exhibited higher thyroid hormone sensitivity among various obesity phenotypes, even when compared with those with MHNO. A positive association was observed between metabolic abnormality and thyroid hormone sensitivity, while the trend of TSH was observed to be consistent with sensitivity to thyroid hormone indices in discriminating metabolic abnormality. Hence, TSH has the potential to serve as a convenient index for detecting sensitivity to thyroid hormones and further metabolic conditions.

Hypertension, dietary fiber intake, and cognitive function in older adults [from the National Health and Nutrition Examination Survey Data (2011–2014)]

Background

Dietary fiber was associated with hypertension (HYP) and cognitive function, but it was unknown whether the effect of HYP on cognitive function in older adults was modified by dietary fiber intake.

Methods

We recruited 2,478 participants from the 2011–2012 and 2013–2014 National Health and Nutrition Examination Survey (NHANES), with cognitive performance measured by Registry for Alzheimer's disease (CERAD), the Animal Fluency test (AFT), and the Digit Symbol Substitution test (DSST). Multivariate General linear model was used to estimate the interaction between dietary fiber intake and HYP status in association with low cognitive performance.

Results

Among 2,478 participants, 36% was Controlled HYP, 25% was Low uncontrolled HYP, 11% was High uncontrolled HYP, and 86% was low dietary fiber intake. The association between HYP status and DSST impairment differed by dietary fiber intake for those with high uncontrolled HYP compared to those without HYP. Among participants with low dietary fiber intake, those with uncontrolled HYP had higher risk of DSST impairment compared to those without HYP [HYP ≥ 90/140: OR (95% CI), 1.68 (1.15–2.45); HYP ≥ 100/160: OR (95%CI), 2.05 (1.29–3.23)]; however, there was no association between HYP status and DSST impairment among participants with high dietary fiber intake. Moreover, the interaction of HYP status and dietary fiber intake on DSST was close to statistical significance (P for interaction = 0.057).

Conclusions

Uncontrolled HYP was associated with poorer cognitive performance in older adults with low, but not high dietary fiber intake. Sufficient dietary fiber intake might be as a new nutrition strategy for the prevention of cognitive impairment in older adults with uncontrolled HYP.

Adherence to mediterranean diet and the risk of differentiated thyroid cancer in a European cohort: The EPIC study

Background

The Mediterranean diet (MD) has been proposed as a healthy diet with a potential to lower the incidence of several types of cancer, but there is no data regarding thyroid cancer (TC). We investigated the association between MD adherence, and its components, and the differentiated TC risk within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort.

Methods

Over 450,000 men and women from nine European countries were followed up for a mean of 14.1 years, during which 712 differentiated TC cases were identified. Adherence to MD was estimated using the relative MD (rMED) score, an 18-point scale including alcohol, and the adapted rMED (arMED) score, a 16-point scale excluding alcohol. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox regression models adjusted for potential confounding factors.

Results

Adherence to the arMED score was not associated with the risk of differentiated TC (HRhigh vs. low adherence = 0.94, 95% CI: 0.70-1.25; p-trend 0.27), while a suggestive, but non-statistically significant inverse relationship was observed with rMED (HRhigh vs. low adherence = 0.88, 95% CI: 0.68-1.14; p-trend 0.17). Low meat (HRlow vs. high meat intake = 0.81, 95% CI: 0.67-0.99; p-trend = 0.04) and moderate alcohol (HRmoderate vs. non-moderate intake = 0.88, 95% CI: 0.75-1.03) intake were related with lower differentiated TC risk.

Conclusions

Our study shows that a high adherence to MD is not strongly related to differentiated TC risk, although further research is required to confirm the impact of MD and, especially, meat intake in TC risk.

Adherence to the Mediterranean Diet as a Modifiable Risk Factor for Thyroid Nodular Disease and Thyroid Cancer: Results From a Pilot Study

Iodine deficiency is the most important established nutritional risk factor for the development of thyroid nodular disease. Nevertheless, to the best of our knowledge, to date no study focused on the association between the adherence to the Mediterranean diet (MD) and thyroid nodular disease. Adherence to the MD was evaluated using the PREvención con DIetaMEDiterránea (PREDIMED) questionnaire. Physical activity, smoking habits, and anthropometric parameters were studied. PREDIMED was used to evaluate the degree of adherence to the MD. Evaluation of fine needle aspiration cytology of thyroid lesions based on 2013 Italian thyroid cytology classification system. Cytology of thyroid nodules was carried out through sonography-guided fine-needle aspiration and patients were divided into 5 categories: TIR2, TIR3a, TIR3b, TIR4, and TIR5. The study population consisted of 794 subjects (554 females, 69.8%), aged 18–65 years, with BMIs ranging from 19.4 to 55.3 kg/m². Thyroid nodular disease was present in 391 participants (49.2%), and the most frequent cytological categories was TIR2 (18.3 %), followed by a TIR4 (8.9 %). The presence of thyroid nodules was also significantly associated with the lowest adherence to the MD (OR 6.16, p < 0.001). Patients with TIR5 had the lower adherence to the MD (2.15 ± 1.12 score) compared to other TIRs (p < 0.001). The cytological category with high-risk of malignancy (TIR4/TIR5) was significantly associated with the lowest adherence to the MD (OR 137.55, p < 0.001) and PREDIMED score (OR = 0.33, p < 0.001, 95% IC = 0.26–0.41, R² = 0.462). At multiple regression analysis, PREDIMED score was the main predictor of both the presence of nodules (p < 0.001) and the cytological category with high-risk of malignancy (p < 0.001). At ROC analysis PREDIMED score ≤ 5 and ≤ 4 (p = 0.001) were the values that predicted the presence of thyroid nodular disease and cytological category with high-risk of malignancy, respectively. In conclusion, our study demonstrated that the low adherence to the MD is associated with the presence of thyroid nodular disease and in particular with those at high-risk of malignancy.

Insulin resistance attenuates the impact of levothyroxine on thyroid autoimmunity and hypothalamic-pituitary-thyroid axis activity in women with autoimmune subclinical hypothyroidism

Subjects with both subclinical hypothyroidism and autoimmune thyroiditis are frequently diagnosed with metabolic syndrome. The purpose of the current study was to investigate whether insulin sensitivity determines levothyroxine action on thyroid antibody titres and hypothalamic-pituitary-thyroid axis activity in young women with autoimmune subclinical hypothyroidism. The study population consisted of three age-, thyroid antibody- and thyrotropin-matched groups of women with autoimmune subclinical hypothyroidism: metformin-naive women with insulin resistance (group A, n=31), women receiving metformin treatment because of insulin resistance (group B, n=32), as well as metformin-naive women with normal insulin sensitivity (group C, n=35). Throughout the study, all subjects were treated with levothyroxine. Titres of thyroid peroxidase and thyroglobulin antibodies, as well as circulating levels of glucose, insulin, lipids, thyrotropin, free thyroid hormones, prolactin, high-sensitivity C-reactive protein (hsCRP) and 25-hydroxyvitamin D were determined at the beginning of the study and 6 months later. Except for two individuals, all patients completed the study. At baseline, group A differed from groups B and C in circulating levels of glucose, HDL-cholesterol, triglycerides, hsCRP, 25-hydroxyvitamin D and the homeostatic model assessment 1 of insulin resistance (HOMA1-IR). Although levothyroxine reduced thyroid antibody titres, decreased thyrotropin levels and increased free thyroid hormone levels in all studied groups, the effect on antibody titres and thyrotropin levels was more pronounced in groups B and C than in group A. The impact of levothyroxine on thyroid antibody titres correlated with baseline and treatment-induced changes in HOMA1-IR, thyrotropin, hsCRP and 25-hydroxyvitamin D. The results of the current study suggest that the impact of exogenous levothyroxine on thyroid autoimmunity and hypothalamic-pituitary-thyroid axis activity is determined by insulin sensitivity.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

Thyroid hormones are necessary for the normal functioning of physiological systems. Therefore, knowledge of any factor (whether genetic, environmental or intrinsic) that alters the levels of thyroid-stimulating hormone (TSH) and thyroid hormones is crucial. Genetic factors contribute up to 65% of interindividual variations in TSH and thyroid hormone levels, but many environmental factors can also affect thyroid function. This review discusses studies that have analyzed the impact of environmental factors on TSH and thyroid hormone levels in healthy adults. We included lifestyle factors (smoking, alcohol consumption, diet and exercise) and pollutants (chemicals and heavy metals). Many inconsistencies in the results have been observed between studies, making it difficult to draw a general conclusion about how a particular environmental factor influences TSH and thyroid hormone levels. However, lifestyle factors that showed the clearest association with TSH and thyroid hormones were smoking, body mass index (BMI) and iodine (micronutrient taken from the diet). Smoking mainly led to a decrease in TSH levels and an increase in triiodothyronine (T3) and thyroxine (T4) levels, while BMI levels were positively correlated with TSH and free T3 levels. Excess iodine led to an increase in TSH levels and a decrease in thyroid hormone levels. Among the pollutants analyzed, most studies observed a decrease in thyroid hormone levels after exposure to perchlorate. Future studies should continue to analyze the impact of environmental factors on thyroid function as they could contribute to understanding the complex background of gene-environment interactions underlying the pathology of thyroid diseases.

A Clinical Trial for the Identification of Metabolic Biomarkers in Hashimoto’s Thyroiditis and in Psoriasis: Study Protocol

Hashimoto’s thyroiditis and psoriasis are inflammatory disorders that significantly impact patients’ quality of life, stressing the need for novel biomarkers of early diagnosis. This randomized clinical trial (NCT04693936) aims to identify Hashimoto’s thyroiditis’ and psoriasis’ metabolic biomarkers and to investigate the effect of environmental factors on the disease-related metabolic imprint and quality of life. Patients with Hashimoto’s thyroiditis, patients with psoriasis, and healthy individuals aged 18–60 will be recruited, enrolled according to eligibility criteria (medical history, clinical thyroid markers and the PASI score) and randomized to two groups. The intervention group will receive a combination of nutraceuticals for 6 months as part of a Mediterranean diet, and the control group will follow their usual diet. Data will be collected at baseline and the end of the study, including metabolite levels, lifestyle and anthropometric measurements, adherence to the Mediterranean diet (through the Mediterranean Diet Score) and disease-specific quality of life (through the Thyroid Patient Report Outcome for Hashimoto’s group, and the Dermatology Life Quality Index for the psoriasis group). This study will investigate metabolic biomarkers and related changes in Hashimoto’s thyroiditis and psoriasis and evaluate the association of metabolic changes with dietary factors and quality of life.

Impact of the Level of Adherence to Mediterranean Diet on the Parameters of Metabolic Syndrome: A Systematic Review and Meta-Analysis of Observational Studies

High adherence to the Mediterranean diet (MD) has been associated with a lower prevalence of Metabolic Syndrome (MetS). The present study aimed to investigate the impact of MD adherence on parameters of MetS. A systematic literature search was performed in PubMed, Cochrane Central Registry of Clinical Trials (CENTRAL), Scopus, EMBASE, Web of Science and Google Scholar databases. Observational studies that recorded adherence to MD and components/measures of the MetS, such as waist circumference (WC), blood pressure (BP), fasting blood glucose (FBG), high-density lipoprotein (HDL) cholesterol and triglycerides (TG), were included in this study. A total of 58 studies were included in our study. WC and TG were significantly lower in the high adherence MD group (SMD: −0.20, (95%CI: −0.40, −0.01), SMD: −0.27 (95%CI: −0.27, −0.11), respectively), while HDL cholesterol was significantly higher in the same group (SMD: −0.28 (95%CI: 0.07, 0.50). There was no difference in FBG and SBP among the two groups (SMD: −0.21 (95%CI: −0.54, 0.12) & SMD: −0.15 (95%CI: −0.38, 0.07), respectively). MD may have a positive impact on all parameters of MetS. However, further research is needed in this field.