Does Dietary Sugar Intake Increase Glaucoma Risk? A Systematic Review and Meta-analysis Blueprint

This audio article is from VisualFieldTest.com.Read the full article here: https://visualfieldtest.com/en/does-dietary-sugar-intake-increase-glaucoma-risk-a-systematic-review-and-meta-analysis-blueprintTest your visual field online: https://visualfieldtest.comSupport the show so new episodes keep coming: https://www.buzzsprout.com/2563091/supportExcerpt:Does Dietary Sugar Intake Increase Glaucoma Risk? A Systematic Review and Meta-analysis Blueprint Introduction Whether dietary sugar contributes to glaucoma risk remains uncertain. The available research is limited and does not consistently measure added sugar itself. Some studies have examined total carbohydrate intake, low-carbohydrate dietary patterns, processed sweets, or ultra-processed foods instead. For example, a prospective Spanish cohort found that participants with the highest total carbohydrate intake had a higher risk of newly diagnosed glaucoma, although no individual carbohydrate food group was clearly responsible. () In contrast, a large analysis of three United States cohorts found no clear association between overall low-carbohydrate dietary scores and primary open-angle glaucoma, although a vegetable-based low-carbohydrate pattern showed a possible association with a specific visual field-loss subtype. () A small case-control study also reported that patients with primary open-angle glaucoma consumed more sweets containing processed sugar than controls, but its retrospective design leaves substantial potential for recall bias and residual confounding. () A 2024 scoping review concluded that most glaucoma nutrition studies relied on food frequency questionnaires and that only a small number of prospective studies had examined carbohydrate-related exposures. () This protocol is designed to determine whether total sugar, added sugar, free sugar, sugary beverages, total carbohydrate, glycemic load, or glycemic index are associated with: Incident primary open-angle glaucoma Change in intraocular pressure Retinal nerve fiber layer loss or glaucoma progression The review should estimate associations carefully without implying that sugar causes glaucoma. Dietary studies are vulnerable to measurement error, confounding, reverse causation, and differences in glaucoma diagnosis. --- Review Objective and Research Question Primary research question Among adults, is higher habitual intake of dietary sugar or sugar-related exposures associated with a greater risk of developing glaucoma or experiencing glaucoma-related structural or pressure changes? Secondary research questions The review should determine: Whether associations differ between added sugar, total sugar, free sugar, and sugar-sweetened beverages Whether glycemic load or glycemic index shows a stronger relationship than sugar grams alone Whether associations differ according to baseline diabetes status Whether findings differ between primary open-angle glaucoma, normal-tension glaucoma, high-tension glaucoma, exfoliative glaucoma, pigmentary glaucoma, and primary angle-closure glaucoma Whether associations are stronger for glaucoma incidence or for disease progression How much results are affected by adjustment for diabetes, body mass index, blood pressure, and total energy intake Whether food frequency questionnaire measurement error may have weakened or distorted reported associations Prespecified causal estimands Because diabetes, body mass index, blood pressure, and total energy intake may play different roles in the causal pathway, the review should distinguish between two related but different questions: Total dietary association: Does a higher sugar exposure relate to glaucoma risk through all plausible pathways, including pathways involving weight gain, diabetes, blood pressure, and vascular or metabolic changes? Metabolic-independent association: Does sugar remain associated with glaucoma after adjustment for diabetes, body mass index, and blood pressure? The second estimate should not be described as the total effect of sugar. It is better described as a conditional or metabolically adjusted association, because adjustment may remove part of the pathway through which diet could influence eye health. --- Eligibility Criteria Population Include studies of: Human adults aged 18 years or older General population samples Occupational or community-based cohorts Patients with ocular hypertension or established glaucoma Participants with or without diabetes Studies involving children may be included in a separate exploratory analysis if sufficient evidence exists, but they should not be pooled with adult studies. Eligible study designs Include: Prospective cohort studies Longitudinal population-based studies Nested case-control studies within prospective cohorts Case-control studies in which dietary exposure was assessed for a period before glaucoma diagnosis or progression Retrospective analyses only if dietary exposure clearly preceded the outcome and the study provides usable effect estimates Prospective studies should be the main evidence base for incidence and progression. Case-control studies should be synthesized separately because their exposure measurement is more vulnerable to recall and selection bias. Required exposure timing The exposure must be measured: Before glaucoma diagnosis Before the progression period being studied Or repeatedly during follow-up in a way that permits a time-ordered analysis Studies measuring diet and glaucoma at the same visit should be excluded from the primary quantitative synthesis because they cannot establish whether dietary exposure preceded the disease. They may be retained for narrative context. Required outcome information Studies must report at least one of the following: Incident glaucoma Change in intraocular pressure Retinal nerve fiber layer loss Glaucoma progression Visual field progression Optic nerve or neuroretinal rim progression Studies must provide a relative risk, hazard ratio, odds ratio, mean difference, annualized rate of change, or enough data to calculate one. Exclude Exclude: Animal or laboratory studies Ecological studies Case reports and case series Studies of blood glucose or glycated hemoglobin without a dietary exposure Studies focused only on diabetic retinopathy Studies that do not distinguish glaucoma from nonspecific visual impairment Studies in which the dietary exposure is a nutritional supplement rather than food or beverage intake Duplicate reports from the same cohort, unless they provide non-overlapping exposure or outcome data If several publications use the same cohort, select the report with the longest follow-up or the most complete outcome ascertainment. Additional reports may be used for subtype or progression analyses without counting participants twice. --- Exposure Definitions Sugar-related exposures must not be treated as interchangeable. The protocol should extract each exposure separately and avoid pooling them unless the definitions are sufficiently comparable. Exposure classification table For the full table, please open this article on visualfieldtest.com. The United States Food and Drug Administration distinguishes total sugars from added sugars: total sugars include sugars naturally present in foods such as fruit and milk, whereas added sugars are incorporated during processing or preparation. () The World Health Organization defines free sugars more broadly to include added sugars and sugars naturally present in honey, syrups, fruit juice, and fruit juice concentrate, while excluding the sugars naturally present in intact fruit, vegetables, and milk. () Sugar-sweetened beverages Sugar-sweetened beverages should be analyzed separately from solid foods because they: Are often consumed quickly May produce a high glycemic exposure Usually provide few or no grams of fiber May be associated with total energy intake and weight gain Can be measured more reliably in some questionnaires than total added sugar Diet beverages should not be combined with sugar-sweetened beverages. They should be analyzed separately as an exploratory exposure because people who choose artificially sweetened drinks may differ systematically from people who do not. One hundred percent fruit juice should also be analyzed separately. It should not automatically be classified as equivalent to either a sugar-sweetened beverage or intact fruit. Glycemic load For studies providing sufficient information, glycemic load should be calculated or extracted as: > Glycemic load = glycemic index × grams of available carbohydrate per serving ÷ 100 Glycemic load reflects both the quality and quantity of carbohydrate. Glycemic index reflects the relative glucose response to a carbohydrate-containing food, whereas glycemic load also accounts for the amount consumed. () Total carbohydrate, glycemic load, and added sugar should not be pooled into a single exposure category. A diet may contain a large amount of carbohydrate from whole grains or legumes but relatively little added sugar. Exposure timing Extract whether exposure was measured: At baseline only As a cumulative average of repeated questionnaires As the most recent diet measure As a change from baseline Using a lagged exposure, such as diet measured two or more years before diagnosis Repeated and cumulative dietary measures should be preferred for chronic outcomes when available because a single questionnaire may not represent long-term dietary habits. --- Outcome Definitions 4.1 Incident primary open-angle glaucoma The primary incidence outcome should be newly diagnoseSupport the show