A Simple Blood Index May Shape Risk of Dementia, Metabolic Disease and Sleep Problems

A routine blood test that costs pennies to perform may carry far more predictive power than clinicians have traditionally assumed. In a sweeping genetic epidemiology study published in Molecular Genetics and Genomics, researchers report that the C-reactive protein–albumin–lymphocyte index, known as the CALLY index, is not merely a passive marker of a patient’s current state. Instead, the analysis suggests that genetically elevated levels of this composite measure are causally linked to a lower risk of Alzheimer’s disease, Alzheimer’s dementia, unspecified dementia and disorders of lipid metabolism, while also revealing an unexpected and more troubling association with an increased risk of sleep disorders. The findings, drawn from hundreds of thousands of participants in the UK Biobank and the FinnGen cohort, position the CALLY index as a candidate tool for disease risk stratification that spans neurology, metabolism and sleep medicine.

The CALLY index first attracted attention in surgical oncology, where studies of patients undergoing gastrectomy for gastric cancer, hepatectomy for colorectal liver metastases and surgery for oral cavity and breast cancers showed that the measure carried prognostic significance for outcomes. Its appeal lies in its elegant simplicity. The index integrates three routinely measured blood components that capture distinct dimensions of a person’s internal physiology: C-reactive protein, an acute-phase protein produced by the liver that rises rapidly during systemic inflammation; albumin, the most abundant plasma protein, whose concentration reflects nutritional status, liver synthetic function and the degree of chronic inflammatory suppression; and the lymphocyte count, a readout of adaptive immune competence. By combining inflammation, nutrition and immunity into a single number, the CALLY index offers a panoramic snapshot of the body’s systemic state that no single biomarker can provide.

What has remained unclear, however, is whether the index merely correlates with disease or whether it plays some causal role in disease development. Observational associations are notoriously vulnerable to reverse causation and confounding. A patient with early neurodegeneration may have poor nutrition and chronic inflammation as consequences of the disease process rather than contributors to it. To cut through this ambiguity, the research team, led by investigators at Soochow University in Suzhou, China, turned to Mendelian randomization, a technique that exploits the random allocation of genetic variants at conception as a form of natural experiment. Because genetic variants inherited from parents are fixed at birth and generally unaffected by later disease processes, they can serve as proxies for a lifelong exposure, allowing researchers to test whether the exposure itself influences disease risk rather than the reverse.

The scale of the underlying data is central to the study’s power. The team first conducted a genome-wide association study of the CALLY index in 265,409 UK Biobank participants, scanning millions of genetic variants across the genome for statistical associations with the composite measure. This effort identified 154 genomic loci significantly associated with the index, providing a rich set of genetic instruments. The loci implicated genes involved in hepatic acute-phase responses, immune cell regulation and metabolic pathways, which is consistent with the three biological pillars the index is designed to capture. The breadth of the signal also confirmed that the CALLY index has a substantial and distributed genetic architecture, a prerequisite for reliable Mendelian randomization analysis.

With the genetic instruments in hand, the researchers performed a phenome-wide association study, or PheWAS, across 713 phenotypes in 113,747 UK Biobank participants. Rather than asking whether one biomarker predicts one disease, a PheWAS inverts the question and asks whether the genetically predicted biomarker is associated with any condition across the entire recorded spectrum of human illness. This agnostic screening approach is designed to surface unexpected connections that hypothesis-driven studies would never think to test. Out of the 713 phenotypes examined, 24 showed statistically significant associations with the genetically predicted CALLY index, a yield that is striking given the stringency of the multiple-testing corrections applied in such analyses.

The most consequential of these associations involved the neurodegenerative outcomes. Higher genetically predicted CALLY index values were linked to lower risks of Alzheimer’s disease, Alzheimer’s dementia and unspecified dementia, and the two-sample Mendelian randomization analysis confirmed these as causal protective effects rather than mere correlations. This finding dovetails with a growing body of evidence implicating systemic inflammation and immune dysfunction in Alzheimer’s pathogenesis. The blood-brain barrier, once viewed as an impenetrable fortress protecting the central nervous system, is now known to be permeable to inflammatory signals arising from systemic infection and chronic low-grade inflammation. Peripheral inflammatory activity can modulate microglial activation within the brain, influence amyloid-beta clearance and shape the trajectory of neurodegeneration. An index that integrates inflammatory burden, nutritional reserve and adaptive immune capacity may therefore capture, in a single measure, several converging pathways that influence the brain’s resilience against degenerative disease.

The metabolic findings reinforce this systems-level interpretation. The PheWAS and subsequent causal analyses linked higher CALLY index values to lower risks of lipid metabolism disorders, and pleiotropy analyses pointed to shared biological pathways in lipid metabolism and inflammation connecting the index to its disease outcomes. Chronic low-grade inflammation is a well-established feature of obesity, insulin resistance and dyslipidemia, and inflammatory cytokines released from adipose tissue can perturb hepatic lipid handling and accelerate atherosclerotic processes. Albumin, meanwhile, is a major carrier protein for fatty acids and other lipophilic molecules in the circulation, and its concentration is sensitive to both nutritional intake and inflammatory catabolism. The convergence of these signals suggests that the CALLY index functions as a barometer of the inflammatory-metabolic axis, a physiological axis whose dysfunction is increasingly recognized as a common root of multiple chronic diseases of aging.

Not every association in the study was reassuring. The Mendelian randomization analysis indicated a causal association between higher genetically predicted CALLY index and increased risk of sleep disorders, a finding that adds an intriguing and cautionary dimension to the biomarker’s profile. Sleep disturbance is itself tightly intertwined with inflammation and immune function; insufficient or fragmented sleep elevates inflammatory markers, while chronic inflammation disrupts the hypothalamic circuits that regulate circadian rhythm. The direction of the observed association, in which a more favorable inflammatory-nutritional-immune profile paradoxically accompanies greater sleep disorder risk, will require further investigation to disentangle. It may reflect shared genetic pathways, compensatory physiological responses or pleiotropic effects of the instrument variants that influence both the index and sleep biology through independent routes. The authors addressed this concern with a battery of sensitivity analyses, including linkage disequilibrium score regression and pleiotropy testing, designed to detect and correct for horizontal pleiotropy, the phenomenon in which genetic variants affect outcomes through pathways other than the exposure of interest.

The methodological rigor underpinning these conclusions deserves emphasis. Two-sample Mendelian randomization relies on three core assumptions: the genetic instruments must be strongly associated with the exposure, must not be confounded by population stratification or other environmental factors, and must influence the outcomes only through the exposure. Violations of the third assumption, known as pleiotropy, are the principal threat to validity, and the study deployed multiple complementary tests, including Egger regression-based approaches, to detect directional pleiotropic bias. The use of two independent data sources, with the UK Biobank supplying the exposure and outcome data and FinnGen providing replication material, further strengthens the case that the observed causal signals are not artifacts of a single cohort’s idiosyncrasies. The ethical framework of the underlying resource was also robust, with approval from the Northwest Multi-center Research Ethics Committee and informed consent from all participants.

The practical implications extend beyond the laboratory. Because the CALLY index is computed from three tests that are already part of standard clinical blood panels, it could be incorporated into risk prediction models at essentially no additional cost. If future prospective studies validate the causal relationships reported here, the index could help clinicians identify individuals whose inflammatory-nutritional-immune profile places them at elevated risk of dementia or metabolic disease decades before symptoms emerge, opening a window for preventive interventions targeting inflammation, nutrition and immune health. At the same time, the sleep disorder finding is a reminder that systemic physiology is a web of trade-offs rather than a simple gradient from good to bad. The study’s authors, supported by funding from the Natural Science Foundation of China, frame the CALLY index as a promising integrated biomarker for disease risk stratification and public health applications, and this phenome-wide genetic analysis provides the strongest evidence yet that the number scrawled on a routine lab report may quietly encode a person’s vulnerability to some of the most burdensome diseases of our time.

Subject of Research: Causal associations between the CRP–albumin–lymphocyte (CALLY) index and multisystem human diseases using phenome-wide Mendelian randomization

Article Title: CRP–albumin–lymphocyte index and multisystem diseases: a phenome-wide Mendelian randomization study

Article References: Niu, B., Xia, M.-H., Wu, J.-X., He, P., Bo, L., Wu, H.-Y., Lei, S.-F., & Deng, F.-Y. (2026). CRP–albumin–lymphocyte index and multisystem diseases: a phenome-wide Mendelian randomization study. Molecular Genetics and Genomics, 301(1), Article 199. https://doi.org/10.1007/s00438-026-02513-0

Image Credits: AI Generated

DOI: 10.1007/s00438-026-02513-0

Keywords: CALLY index, Mendelian randomization, PheWAS, GWAS, Alzheimer's disease, dementia, lipid metabolism, sleep disorders, inflammation, biomarkers, UK Biobank, FinnGen