A cross-sectional study investigating the impact of dietary vitamin D intake and fortification in Jordanian adults with type 2 diabetes

Background: Vitamin D is crucial in maintaining bone strength and supporting immune function and mayalso influence metabolic health, including glycemic control. This study aimed to investigate the relationshipbetween the vitamin D intake and markers of glycemic health in Jordanian adults with type 2 diabetes mellitus(T2DM). Methods: This cross-sectional study was conducted on 240 patients with T2DM aged 42–69 years. Conveniencesampling was used to recruit participants from hospitals across Jordan. Participants with conditions or med-ications impacting vitamin D status (e.g. celiac disease and antiepileptic drugs) were excluded from the study.Data on demographics, medical history, lifestyle, and dietary intake were collected using a structured ques-tionnaire. Liquid chromatography with tandem mass spectrometry analysis was used to estimate the vitaminD content of commonly consumed foods. Serum 25(OH)D and glycated hemoglobin (HbA1c) levels weremeasured. Normality was tested using the Shapiro-Wilk test. Pearson’s correlation and analysis of variance(ANOVA) were used to determine links between the dietary vitamin D intake, serum vitamin D levels, andglycemic outcomes. Results: The mean dietary vitamin D intake was 150 ± 140 international units/day, with tuna, yogurt, pitabread, and non-fortified Ultra-High Temperature (UHT) milk as primary sources. Total dietary vitamin Dintake showed no significant association with fasting blood glucose but was inversely correlated with HbA1c(r = –0.38, P < 0.05). Dairy (r = 0.42, P < 0.05) and fish (r = 0.35, P < 0.05) intakes were positively associatedwith serum 25(OH)D levels (mean: 21.3 ± 4.4 ng/mL), unlike meat, eggs, or bread. Higher income, education,and sun exposure were linked to higher levels of vitamin D in the serum. Vitamin D intake and status werefound to be significantly associated with age, body mass index (BMI), frequency of breakfast consumption,and snack intake. Conclusion: Consuming vitamin D-rich sources, including dairy, fish, and fortified foods, was associated withhigher serum vitamin D levels, which were related to better HbA1c levels. This suggests a potential bene-fit for glycemic control and broader diabetes management. A cross-sectional design makes it impossible to distinguish cause and effect, and factors such as supplement use or varying levels of food fortification com-plicate the interpretation of the results. Longer-term and intervention-based studies are necessary before astronger claim can be made.