Research: here's why excessive sugar consumption can damage the heart

IN BRIEF

• Excess sugar intake may be associated with an increased risk of cardiovascular disease and, in some experimental contexts, with metabolic stress in the heart muscle.
• Experimental studies indicate that intracellular accumulation of glucose-6-phosphate (G6P) in the myocardium is linked to mTOR activation and endoplasmic reticulum stress, conditions that can impair cardiac pump function [1].
• Observational epidemiological evidence finds associations between high consumption of added sugars and increased cardiovascular mortality; however, this research does not automatically establish a direct causal link and is influenced by confounding factors [3][6][7].
• Plausible mechanisms include: accumulation of glycolytic metabolites, increased hepatic lipogenesis (especially for fructose), inflammation, and oxidative stress; these mechanisms are supported by experimental studies and metabolically controlled trials [2][4][5][8].

Abstract: what does science say?

Contemporary research indicates that chronic excess sugar (especially added sugars and sugary drinks) is associated with several factors that increase cardiovascular risk: weight gain, insulin resistance, dyslipidemia, and hepatic steatosis. In experimental settings, in animal models and human tissue, intramyocardial accumulation of glucose-6-phosphate (G6P) has been linked to activation of the mTOR pathway and endoplasmic reticulum stress, conditions that can precede and promote the deterioration of cardiac function. Observational evidence in populations shows associations between high sugar consumption and a greater risk of cardiovascular events and mortality, but the relationship depends on the dose, the form of sugar (e.g., fructose vs. glucose), the individual's metabolic context, and other lifestyle factors. A general recommendation to moderate added sugar intake is therefore justified, while recognizing that definitive proof of causality in human populations requires further studies suitable for controlling confounders and assessing dose-response.

What are sugars and how are they metabolized by the heart?

The "sugars" present in foods include monosaccharides (glucose, fructose) and disaccharides (sucrose). After intestinal absorption, glucose enters cardiac cells via membrane transporters (GLUT) and is rapidly phosphorylated to glucose-6-phosphate (G6P) by hexokinase. G6P is a key metabolite that can follow different pathways: glycolysis to produce energy, glycogen synthesis, or entry into the pentose phosphate pathway (PPP). Under conditions of substrate excess (hyperglycemia, acute high sugar intake) or altered mitochondrial oxidation, G6P can accumulate in the cell. Experimentally, this accumulation has been associated with the activation of nutrient signals (mTOR), endoplasmic reticulum stress, and reduced contractile efficiency in the heart, suggesting that an excess of carbohydrates leading to strong glycolytic fluxes can contribute to metabolic stress in the myocardium [1].

What is the experimental evidence on cardiac mechanisms?

G6P, mTOR, and endoplasmic reticulum stress

Studies in animal models and human tissues show that G6P accumulation in the myocardium is associated with mTOR pathway activation and markers of endoplasmic reticulum stress; these processes can reduce contractile function and precede pathological left ventricular remodeling [1]. In experiments, mTOR inhibition with rapamycin or metabolic modulation with metformin attenuated these effects, indicating a plausible biological link between glucose metabolism and cellular signaling that regulates growth and protein homeostasis [1].

Role of the pentose phosphate pathway and hexokinase

Hexokinase (HK2) regulates the initial conversion of glucose to G6P; experimentally, an increase in flux towards the pentose phosphate pathway can modulate oxidative stress and cardiac hypertrophy. Studies of cardiac HK2 overexpression show that modifying this metabolic flux influences ROS levels and the response to increased load, suggesting that the direction of glucose carbon (glycolysis vs. PPP) is crucial for the functional outcomes of the heart muscle [2].

What do epidemiological studies show?

Large observational analyses in populations indicate an association between high consumption of added sugars (particularly sugary drinks) and a greater risk of cardiovascular events and cardiovascular mortality [3][6]. Meta-analyses and systematic reviews report a dose-response relationship for some categories of cardio-metabolic outcomes: each additional daily serving of sugary drink has been associated with an increased risk of certain cardiometabolic events in several syntheses of evidence [6]. Specific cohort studies have found associations with mortality and the onset of cardiovascular diseases independent of traditional factors, while recognizing the influence of overlaps with obesity, hypertension, and diabetes [3][7].

Sugary drinks, fruit, and juices

Evidence often distinguishes sugary drinks (including juices and fruit-based beverages with added sugars) from other carbohydrate sources: liquid beverages can provide rapid caloric intake and less energy compensation, promoting weight gain and associated dysmetabolism; trials and prospective studies report adverse metabolic effects of fructose and some sugary drinks under conditions of high consumption [4][5][6]. However, the strength of the association can vary depending on the type of beverage, the population studied, and adjustments for confounding variables.

Limitations of the evidence

It is important to distinguish between observational association and causal proof. Population studies are vulnerable to residual confounding, imprecise dietary measurement, and behavioral changes over time. Controlled metabolic trials document mechanisms and physiological responses, but often use high doses over a short period and limited samples, with different implications compared to chronic exposure in the population. Furthermore, the metabolic response depends on the dose, the type of sugar (glucose vs. fructose), the metabolic context (presence of obesity or diabetes), and the overall dietary accompaniment. Therefore, interpretation must remain cautious: the evidence is consistent with a harmful role of excess sugars in promoting risk factors and biological mechanisms favoring cardiac damage, but definitive proof of causality for heart failure in the population requires additional studies and long-term interventions.

What it means in practice

For the non-clinical reader: research suggests that reducing added sugar intake—especially in the form of sugary drinks—is a reasonable choice to limit metabolic risk factors that, over time, increase cardiovascular risk. This does not imply that small, occasional amounts are necessarily harmful, but that the habit of high and repeated consumption can promote adverse metabolic processes (G6P accumulation in tissues, insulin resistance, increased lipogenesis) that contribute to obesity, dyslipidemia, and systemic inflammation [1][4][5]. For individuals with pre-existing cardiovascular conditions or hypertension, overall diet and risk factor control remains essential; any significant dietary changes should be discussed with a healthcare professional. Finally, pay attention to labels: many processed products contain added sugars or starches that increase the total intake of assimilable carbohydrates.

Key takeaways

• Chronic excess of added sugars is associated with worsening cardiovascular risk factors (weight, lipids, insulin resistance) and increased cardiovascular mortality in observational studies [3][6][7].
• Experimental mechanisms link intramyocardial G6P accumulation to mTOR activation and endoplasmic reticulum stress, potential pathways that precede cardiac functional deterioration [1].
• Dietary fructose has metabolic peculiarities that promote hepatic lipogenesis and can increase cardiometabolic risk if consumed in excess [4][5].
• The evidence includes both well-controlled experimental studies and large observational cohorts; both sources are informative but have distinct limitations that require cautious interpretation.
• Reasonable and contextualized dietary changes (reduction of sugary drinks and added sugars) can help reduce risk factors without the need for extreme or immediate measures.

Editorial conclusion

In recent years, the literature has focused on both concrete biological signals and consistent epidemiological associations between excess sugar and cardiovascular risk. The proposed mechanism involving glucose-6-phosphate accumulation and subsequent activation of nutrient pathways (mTOR) offers a plausible biological explanation for the heart's vulnerability under conditions of metabolic overload [1][2]. However, translating these experimental data into public health recommendations requires judgment that considers dose, form of sugar, individual context, and overall diet quality. For readers, the most prudent strategy based on current evidence is to moderate added sugar intake, prioritize minimally processed foods, and consult healthcare professionals for personalized guidance.

Editorial note

This article is based on past research and communications and has been updated according to criteria of clarity, scientific rigor, and accessible language. The content is for informational purposes only and does not replace specialist medical advice. For clinical questions or therapeutic decisions, consult your doctor.

SCIENTIFIC RESEARCH

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2. McCommis KS, Douglas DL, Krenz M, Baines CP. Cardiac‑specific hexokinase 2 overexpression attenuates hypertrophy by increasing pentose phosphate pathway flux. J Am Heart Assoc. 2013;2(6):e000355. https://doi.org/10.1161/JAHA.113.000355 [2]
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