Abstract
ABSTRACT
Introduction
Until now, the thyroid cancer case number has increased, and it is not entirely possible to attribute this continuous growth to more meticulous thyroid nodule selection and more accurate diagnostic techniques. While there is currently no conclusive evidence linking dietary factors to thyroid cancer, certain dietary patterns seem to have an impact on the development of the disease. There are interesting connections among diet, environment, metabolism and thyroid carcinogenesis; a deeper comprehension of the underlying mechanisms should help the identification of modifiable risk factors for thyroid cancer. This protocol aims to guide a systematic review and meta-analysis of the literature to search for an association between dietary pattern and risk of thyroid cancer.
Methods and analysis
The databases to search for observational studies will be PubMed, Embase, Scopus, Web of Science and LILACS, from inception to 10 December 2024. No language limitation or publication period will be imposed. The outcome will be the patients with thyroid cancer. Three impartial reviewers will choose the studies and extract data from the original publications. The Newcastle-Ottawa Quality Scale will assess the risk of bias, and the certainty of the evidence will be achieved by using the Grading of Recommendations Assessment, Development and Evaluation. The R (V.4.3.1) will be performed for data synthesis, and to measure heterogeneity, we will compute the I2 statistics. Additionally, a quantitative synthesis will be performed if the included studies are sufficiently homogenous.
Ethics and dissemination
It is not necessary to acquire ethical approval, as this study will be a review of the published data. A peer-reviewed publication will publish the systematic review’s findings.
PROSPERO registration number
International Prospective Register of Systematic Reviews (PROSPERO) CRD 42023463802.
Keywords: ONCOLOGY, Thyroid disease, NUTRITION & DIETETICS
Strengths and limitations of this study.
The search strategy was developed based on a validated search strategy by an expert librarian and information specialist.
The manuscript proposes an updated review of observational research studies, and this systematic review addresses an important gap in the current evidence.
We will collect a wide range of results to assess the potential risks of thyroid cancer associated with dietary patterns.
Both the quality of the included literature and the outcomes will be evaluated.
A variety of control interventions and differences in sample size, time of exposure and population may increase heterogeneity and bias.
Introduction
Thyroid cancer (TC) represents the most frequent endocrine malignancy.1 Over the previous 40 years, the incidence has climbed globally.2 Although TC constitutes only 1% of all epithelial malignancies, it represents 95% of all endocrine cancers.3
According to GLOBOCAN 2020, estimates of cancer incidence and mortality produced by the International Agency for Cancer Research, the incidence of TC was 586 202 cases.4
Such constant growth cannot be fully attributed to more intensive selection of the thyroid nodule and more sensitive diagnostic procedures.1 Therefore, it has been proposed that environmental factors, lifestyle and comorbidities could contribute to this phenomenon.5 It seems that environmental variables are a major element in the development of TC. In addition, certain foods and illnesses connected to overfeeding, such as obesity, should be considered modifiable risk factors with several TC risk factors, with dietary practices and nutritional aspects receiving special focus.1
In recent years, some studies6 7 have demonstrated an association between macronutrient ingestion and tumour susceptibility. The underlying mechanisms of these associations have not been completely clarified, but it has been suggested that carbohydrate consumption could promote insulin resistance and that protein intake is related to an increased risk of developing cancer because of the high nitrosamine content in some processed meat products. The relationships between macronutrients consumption and TC risk have recently been investigated.5
Overall, there has been a lot of interest in dietary patterns as potential promoters and modifiable risk factors for TC. In previous study, high consumption of certain fatty foods was associated with an increased risk; the analysis of the current diet showed a positive result. A diet high in calories is closely linked to weight gain and high body weight, both of which have been linked to an increased risk of TC, especially in women who consume large amounts of butter and cheese.8 It should be noted that there was no proof that drinking alcohol increased the risk of TC. Consuming fruit has been associated with a lower risk of thyroid disease, and research suggests that eating a lot of fruit and vitamin C can protect against many types of epithelial cancer.8
The present protocol searches conduct a systematic review and meta-analysis into the existence of evidence about the risk factors for TC linked to dietary patterns.
Review questions?
Are there associations between dietary patterns and the risk of TC?
Objectives
The main purpose of this systematic review and meta-analysis is to evaluate the dietary pattern as a risk factor for TC.
Materials and methods
The Meta-analysis of Observational Studies in Epidemiology9 and the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA)10 11 criteria will be followed in the production of the systematic review and meta-analysis under consideration. The International Prospective Registry of Systematic Reviews (PROSPERO) (CRD42023463802) has a reference to this protocol. The starting date of Protocol is 10 September 2023, and it is expected to conclude the systematic review by 10 December 2024.
Inclusion criteria
The systematic review and meta-analysis consist of the following studies: observational studies (cohort, cross-sectional and case-control); studies involving patients (age >18) with TC; studies without time restriction and studies published in any language.
Exclusion criteria
Meeting abstracts, case reports, review papers, publications in books, theses and commentaries.
The Population, Exposure, Control, Outcome and Types of studies (PECOT) strategy
Population: adults (>18 years).
Exposure: unhealthy dietary pattern.
Control: healthy dietary pattern.
Outcome: TC.
Types of studies: observational studies (cohort, cross-sectional and case-control).
Types of patients
Studies involving patients aged >18 with TC.
Types of exposures
Studies involving patients with unhealthy dietary patterns.
Types of outcome measures
TC is an important health problem for this population.
Patient and public involvement
This is a protocol for a systematic review and meta-analysis; no individual patient data will be included; instead, the research will be carried out using a broad and thorough literature search from pertinent databases. Therefore, when choosing the search parameters, choosing the outcome metrics, carrying out the study design and interpreting the findings, patients will not be involved.
Search strategy
Important electronic databases such as PubMed, Embase, Scopus, Web of Science and LILACS will be searched. No language or publication period restrictions will be imposed. The grey literature will not be searched. The reference lists of all eligible articles will be manually searched to identify any additional relevant citations to ensure a comprehensive search.
The Medical Subject Headings terms will be: (Behavior, Eating OR Behavior, Feeding OR Behavior, Feeding-Related OR Diet Habit OR Dietary Habit OR Eating Behavior OR Eating Habit OR Feeding Behaviors OR Feeding Pattern OR Feeding Related Behavior OR Feeding-Related Behavior OR Food Habit OR Habit, Diet OR Habit, Dietary OR Habit, Eating OR Habit, Food OR Pattern, Feeding OR Diet, Meat-Sweet OR Diet, Occidental OR Dietary Pattern, Western OR Diets, Meat-Sweet OR Diets, Western OR Meat Sweet Diet OR Meat-Sweet Diet OR Occidental Diet OR Pattern, Western Dietary OR Western Diet OR Western Dietary Pattern) AND (Adenoma, Thyroid OR Cancer of the Thyroid OR Cancer of Thyroid OR Cancer, Thyroid OR Carcinoma, Thyroid OR Neoplasm, Thyroid OR Radioiodine-Refractory Thyroid Cancer OR Thyroid Adenoma OR Thyroid Cancer OR Thyroid Carcinoma OR Thyroid Neoplasm) AND (Observational Study OR Cohort Studies OR Retrospective Studies) (table 1). The librarian with expertise in electronic searching participated in the development of the search strategy.
Table 1. The search strategy for Medline/PubMed.
| Search items | |
| 1 | Behavior, Eating |
| 2 | Behavior, Feeding |
| 3 | Behavior, Feeding-Related |
| 4 | Diet Habit |
| 5 | Dietary Habit |
| 6 | Eating Behavior |
| 7 | Feeding Behaviors |
| 8 | Feeding Pattern |
| 9 | Feeding Related Behavior |
| 10 | Feeding-Related Behavior |
| 11 | Food Habit |
| 12 | Habit, Diet |
| 13 | Habit, Dietary |
| 14 | Habit, Eating |
| 15 | Habit, Food |
| 16 | Pattern, Feeding |
| 17 | Diet, Meat-Sweet |
| 18 | Diet, Occidental |
| 19 | Dietary Pattern, Western |
| 20 | Diets, Meat-Sweet |
| 21 | Diets, Western |
| 22 | Meat Sweet Diet |
| 23 | Meat-Sweet Diet |
| 24 | Occidental Diet |
| 25 | Pattern, Western Dietary |
| 26 | Western Diet |
| 27 | Western Dietary Pattern |
| 28 | 1–27/OR |
| 29 | Adenoma, Thyroid |
| 30 | Cancer of the Thyroid |
| 31 | Cancer of Thyroid |
| 32 | Cancer, Thyroid |
| 33 | Carcinoma, Thyroid |
| 34 | Neoplasm, Thyroid |
| 35 | Radioiodine-Refractory Thyroid Cancer |
| 36 | Thyroid Adenoma |
| 37 | Thyroid Cancer |
| 38 | Thyroid Carcinoma |
| 39 | Thyroid Neoplasm |
| 40 | 29–39/OR |
| 41 | 28 AND 40 |
Other sources
Eligible studies may also be chosen from the reference lists of retrieved papers. That is, the scope of the computerised literature search may be expanded based on the reference lists of retrieved publications.
Data collection and analysis
Selection of studies
Three authors, YGN, AAS and CXA, will independently screen the search results using titles and abstracts, using the software Rayyan (https://www.rayyan.ai). Duplicates and reviews will be eliminated from the database. The full text will be reviewed by the same authors, and they will determine whether the studies meet the inclusion criteria. The articles will be included in an Excel table (Google Drive). A fourth reviewer, MMGDL, will resolve any inconsistencies. The selection of studies will be summarised in a PRISMA flow diagram (figure 1).
Figure 1. PRISMA flow diagram for systematic review and meta-analysis. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-analyses.
Data extraction and management
A data extraction form will be developed and tested, according to the recommendations of the Cochrane instrument. Data from each included study will be extracted independently by two reviewers (YGN and AAS), and any subsequent discrepancies will be resolved through discussion with a third reviewer (CXA). The data extracted will include information on the year of publication, authors, study location, the type of study, population (including age and sex), main objectives, eligibility criteria and dietary pattern.
Addressing missing data
In the event of missing data, the authors of this article will contact the corresponding authors or coauthors of this article by phone or email. If we do not obtain the required details, the data will be excluded from our analysis and will be covered in the discussion section.
Risk of bias assessment
Two independent researchers will examine the quality of the articles (YGN and AAS) using the Newcastle-Ottawa Quality Scale.12
Assessment of heterogeneity
A standard χ2 test will be used to assess the heterogeneity between the study results at a significance level of p<0.1. We intended to compute the I2 statistic, a quantitative indicator of study inconsistency, in order to evaluate heterogeneity. Heterogeneity will only be evaluated if a meta-analysis is warranted. The I2 statistic <25% represented low heterogeneity, 25%–50% represented moderate heterogeneity and >50% represented high heterogeneity. In cases where there was substantial heterogeneity in the included studies (I2>50%), the random-effects model will be applied, and when low heterogeneity exists in the included studies, the fixed-effects model will be used.13
Analysis
The data will be entered into the R software (V.4.3.1). This software enables users to input protocols; include text; complete reviews; study characteristics, comparison tables and study data; and perform meta-analyses. We will extract or calculate the OR and 95% CI for each study, for dichotomous results.
Sensitivity analysis will be used to explore the robustness of the findings regarding study quality and sample size. We can only do this if a meta-analysis is performed. Sensitivity analysis will be presented in a summary table.
If the meta-analysis cannot be completed for all or some of the included studies, the remaining research characteristics and findings will be summarised narratively.
Grading quality of evidence
The certainty of the evidence will be assessed using the Grading of Recommendations Assessment, Development and Evaluation14 method, or an equivalent methodology will be clearly described and documented.
Ethics and dissemination
Ethical approval is not necessary because this review will draw on publicly available scientific literature. The results of this systematic review will be published in a peer-reviewed publication, and if sufficient new evidence becomes available to warrant a revision in the review’s conclusions, updates will be carried out. Any modifications to the protocol made during the review process will be noted in the manuscript.
Acknowledgements
The authors acknowledge the assistance provided by the Postgraduate Program in Health Sciences of the Federal University of Rio Grande do Norte (UFRN), Liga Norte Riograndense Contra o Câncer and Rafaela Carla Melo de Paiva librarian who contributed to the search strategy.
Footnotes
Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Prepublication history for this paper is available online. To view these files, please visit the journal online (https://doi.org/10.1136/bmjopen-2024-085631).
Patient consent for publication: Not applicable.
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient and public involvement: Patients and/or the public were not involved in the design, or conduct, or reporting or dissemination plans of this research.
References
- 1.Barrea L, Gallo M, Ruggeri RM, et al. Nutritional status and follicular-derived thyroid cancer: An update. Crit Rev Food Sci Nutr. 2021;61:25–59. doi: 10.1080/10408398.2020.1714542. [DOI] [PubMed] [Google Scholar]
- 2.Prete A, Borges de Souza P, Censi S, et al. Update on Fundamental Mechanisms of Thyroid Cancer. Front Endocrinol (Lausanne) 2020;11:102. doi: 10.3389/fendo.2020.00102. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Boufraqech M, Patel D, Xiong Y, et al. Diagnosis of thyroid cancer: state of art. Expert Opin Med Diagn. 2013;7:331–42. doi: 10.1517/17530059.2013.800481. [DOI] [PubMed] [Google Scholar]
- 4.International Agency for Research on Cancer . Lyon: IARC; 2023. [01-Dec-2023]. Global cancer observatory; [about 3 screens] c1965. https://gco.iarc.fr/ Available. accessed. [Google Scholar]
- 5.Nettore IC, Colao A, Macchia PE. Nutritional and Environmental Factors in Thyroid Carcinogenesis. Int J Environ Res Public Health. 2018;15:1735. doi: 10.3390/ijerph15081735. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Marcello MA, Sampaio AC, Geloneze B, et al. Obesity and excess protein and carbohydrate consumption are risk factors for thyroid cancer. Nutr Cancer. 2012;64:1190–5. doi: 10.1080/01635581.2012.721154. [DOI] [PubMed] [Google Scholar]
- 7.Markaki I, Linos D, Linos A. The influence of dietary patterns on the development of thyroid cancer. Eur J Cancer. 2003;39:1912–9. doi: 10.1016/s0959-8049(03)00432-5. [DOI] [PubMed] [Google Scholar]
- 8.Galanti MR, Hansson L, Bergström R, et al. Diet and the risk of papillary and follicular thyroid carcinoma: a population-based case-control study in Sweden and Norway. Cancer Causes Control. 1997;8:205–14. doi: 10.1023/a:1018424430711. [DOI] [PubMed] [Google Scholar]
- 9.Stroup DF, Berlin JA, Morton SC, et al. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA. 2000;283:2008–12. doi: 10.1001/jama.283.15.2008. [DOI] [PubMed] [Google Scholar]
- 10.Liberati A, Altman DG, Tetzlaff J, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration. BMJ. 2009;339:b2700. doi: 10.1136/bmj.b2700. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Moher D, Liberati A, Tetzlaff J, et al. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med. 2009;6:e1000097. doi: 10.1371/journal.pmed.1000097. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Wells GA, Shea B, O’Connell D, et al. The newcastle- ottawa scale (nos) for assessing the quality if nonrandomized studies in meta-analyses. [-Nov-2023]. https://www.ohri.ca/programs/clinical_epidemiology/oxford.asp Available. Accessed.
- 13.Higgins J, Thomas J, Chandler J, editors. Cochrane Handbook for Systematic Reviews of Interventions. Oxford: Cochrane Collaboration; c2023. https://training.cochrane.org/handbook/current Available. [Google Scholar]
- 14.Balshem H, Helfand M, Schünemann HJ, et al. GRADE guidelines: 3. Rating the quality of evidence. J Clin Epidemiol. 2011;64:401–6. doi: 10.1016/j.jclinepi.2010.07.015. [DOI] [PubMed] [Google Scholar]