The study was conducted by internists Muhammet Ateş and Barış Karagün of the Department of Internal Medicine at Adana City Training and Research Hospital in Adana, Türkiye. Working from the hospital’s anonymized records, the pair assembled a retrospective cohort of 220 adults admitted for treatment of an infected diabetic foot wound. For every patient, they recorded the admission serum concentration of 25-hydroxyvitamin D, the stable storage form of vitamin D that clinical laboratories use as the standard yardstick of vitamin status. Deficiency was defined, in line with conventional thresholds, as a level below 20 nanograms per milliliter. The prevalence result was arresting: 109 of the 220 patients, or 49.5 percent, were vitamin D deficient on the day of admission. In other words, roughly one in every two patients arriving with a diabetic foot infection was already running on empty reserves of a hormone-like nutrient that immune cells depend on.

Diabetic foot infection is among the most feared complications of diabetes, and its biology explains why. Chronically high blood sugar damages peripheral nerves, so patients lose the protective pain sensation that would normally alert them to a blister or small ulcer early. Meanwhile, diabetes narrows and stiffens the arteries of the leg, starving the wound of the oxygen and immune cells that healing requires. Hyperglycemia also handicaps the defenses directly: neutrophils, the frontline white blood cells that engulf bacteria, move, adhere and kill less efficiently when glucose runs high. The result can be an ulcer that progresses from a superficial sore to a deep, bone-invading infection. To standardize comparisons, the researchers graded every infection using the criteria of the International Working Group on the Diabetic Foot and the Infectious Diseases Society of America, which classify infections as mild, moderate or severe according to depth, extent and the presence of a systemic inflammatory response. In this cohort, 103 patients (46.8 percent) had mild infections, 66 (30.0 percent) moderate and 51 (23.2 percent) severe.

The first biomarker, vitamin D, is less a vitamin than a secosteroid hormone. The 25-hydroxyvitamin D measured in the study is produced in the liver and circulates for weeks as the body’s reservoir; the kidneys and, crucially, immune cells themselves convert it into the active hormone 1,25-dihydroxyvitamin D. Immune cells are not bystanders in this system. Macrophages, dendritic cells and lymphocytes carry vitamin D receptors, and when activated vitamin D binds to them, it switches on genes encoding antimicrobial peptides such as cathelicidin—natural antibiotics that disrupt bacterial membranes—while tempering the release of inflammatory cytokines. Deficiency is especially common in type 2 diabetes: excess adipose tissue sequesters the fat-soluble vitamin, chronic hyperglycemia interferes with its activation, and diabetic kidney impairment can blunt the final activation step. A level below 20 ng/mL, the threshold used here, is conventionally read as frank deficiency—a state in which the immune system may be operating without one of its chemical co-pilots.

The second biomarker family is even cheaper: four inflammation indices computed arithmetically from the standard complete blood count that virtually every admitted patient already receives. The neutrophil-to-lymphocyte ratio divides the absolute neutrophil count by the absolute lymphocyte count, capturing the classic signature of acute physiological stress—neutrophils surge into the circulation under cortisol, catecholamines and interleukin-6, while lymphocytes fall. The platelet-to-lymphocyte ratio adds platelets, which climb as part of the inflammatory response. The systemic immune-inflammation index multiplies platelet count by neutrophil count and divides by lymphocyte count, producing a composite gauge of the combined inflammatory armament. The systemic inflammation response index multiplies neutrophils by monocytes—the cells that sustain and orchestrate chronic inflammation—divided by lymphocytes. Because all four indices can be derived from numbers already printed on any admission blood panel, they cost nothing and can be calculated within minutes of arrival, turning routine laboratory output into an immediate readout of the body’s inflammatory temperature.

When the researchers split the cohort by vitamin D status, the deficient group looked sicker across the board. Body mass index averaged 32.1 versus 29.9 kg/m² in the replete group, and long-term glucose control, gauged by glycated hemoglobin (HbA1c), was substantially worse at 9.1 versus 8.3 percent, with both comparisons significant at p < 0.001. The inflammatory indices told the same story: median NLR was 5.7 (interquartile range 4.3–7.3) in deficient patients versus 3.6 (3.0–5.0) in those with adequate vitamin D, while the systemic immune-inflammation index registered 1774.0 (1282.0–2499.0) versus 1042.0 (812.5–1450.0). The most consequential difference was time: deficient patients spent a median of 14.0 days in hospital (interquartile range 12.0–17.0), compared with 10.0 days (8.0–12.0) for the replete. Severe infection was more than three and a half times as common in the deficient group, affecting 36.7 percent versus 9.9 percent. On every measure captured at the bedside, low vitamin D flagged a patient in deeper trouble.

Equally striking was the graded pattern across infection severity. Moving from mild to moderate to severe disease, mean 25-hydroxyvitamin D stepped down in lockstep, from 22.1 ± 4.8 ng/mL in mild cases to 17.1 ± 4.2 ng/mL in severe ones, while median NLR climbed from 3.3 (2.7–4.0) to 8.2 (6.9–9.1), both trends robust at p < 0.001. In epidemiology, such a dose-response gradient is one of the classic signals that an association may be more than statistical noise: the deeper the infection, the lower the vitamin and the hotter the inflammation. Alongside these group comparisons, the team ran correlation analyses, logistic regression, linear regression and receiver operating characteristic analyses, a statistical battery designed to test whether the raw associations would survive once other clinical variables entered the equation.

The decisive results came from the multivariable models. In adjusted logistic regression, two variables emerged as independently associated with severe infection: the admission NLR, with an adjusted odds ratio of 3.06 per unit increase (95 percent confidence interval 2.09–4.48, p < 0.001), and serum albumin, with an adjusted odds ratio of 0.10 per unit increase (95 percent confidence interval 0.01–0.76, p = 0.026). Albumin, the liver’s most abundant export protein, is a negative acute-phase reactant: its concentration falls as inflammation ramps up, as nutrition falters and as damaged vessels leak protein into tissue. A low albumin therefore works as a composite alarm for catabolism, malnutrition and systemic illness—precisely the terrain on which severe diabetic foot infections flourish. Notably, vitamin D deficiency itself dropped out as an independent predictor of severity once other variables were accounted for. For length of stay, however, deficiency held its ground: in adjusted linear regression, vitamin D deficiency carried a coefficient of 0.192 (95 percent confidence interval 0.112–0.273, p < 0.001) and NLR a coefficient of 0.052 (95 percent confidence interval 0.036–0.068, p < 0.001), meaning both remained associated with longer admissions after correction.

The authors are explicit that these are associations, not verdicts on causation. The study was retrospective and single-center, built on anonymized hospital records from one institution; the protocol was approved by the hospital’s ethics committee in March 2026, with informed consent waived under the anonymized design. Reverse causality is a live possibility: systemic infection and inflammation can themselves disturb vitamin D metabolism and suppress its circulating levels, so a low 25-hydroxyvitamin D reading may partly be a consequence of severe illness rather than a contributor to it. Deficiency could also simply be a proxy for the metabolic storm that surrounds diabetic foot disease—obesity, poor long-term glycemic control, malnutrition and reduced mobility all deplete vitamin D while independently worsening outcomes. Ateş and Karagün accordingly frame their results as hypothesis-generating. Their conclusion draws a careful line: elevated admission NLR and hypoalbuminemia may warrant closer assessment for severe infection, while low 25-hydroxyvitamin D should be interpreted as a marker of overall vulnerability rather than a target that correction alone is guaranteed to fix. No vitamin D supplementation was tested.

Even so, the practical signal is difficult to ignore. The two instruments that carried the strongest associations—a white-cell ratio and a vitamin level—are among the cheapest tests in existence, orderable in any emergency department in the world. If prospective studies replicate these findings, an admission checklist for diabetic foot patients could take shape: calculate the NLR, check the albumin, note the vitamin D. Patients with a high ratio and low protein might be routed toward closer monitoring, earlier imaging for deep involvement and more aggressive initial antimicrobial therapy, while deficient patients could simply be expected to stay longer and be planned for accordingly. The study also feeds a broader scientific current: the search for free, computable inflammation gauges that transform routine blood counts into risk stratification. With diabetes prevalence climbing worldwide and foot disease claiming a heavy share of diabetes-related hospital days, a zero-cost warning system read off numbers clinicians already possess is exactly the kind of simple idea with far reach. Whether restoring vitamin D can shorten those fourteen-day stays is a question only intervention trials can answer.