Cobalamin deficiency, B12 deficiency, macrocytic anemia, megaloblastic anemia, nutritional anemia, vitamin B12 deficiency, PakistanTo examine the associations of sociodemographic factors, comorbidities, diet, medications, vitamin D levels, hematological indices, and symptoms with vitamin B12 status among primary care patients in Karachi, PakistanThis cross-sectional study was conducted in 2023 at the tertiary care hospital. Adults recently tested for vitamin B12 as advised by physicians were enrolled (n=252). Data on demographics, comorbidity, medications, diet, and symptoms were collected through structured interviews, alongside BMI and laboratory results. Associations were analyzed using descriptive statistics, Chi-square, and correlation coefficient, with p<0.05 considered significant.Of 252 participants (71.4% female, median age 46 years), fatigue (79.5%), muscle weakness (73.2%), and numbness/tingling (69%) were the most frequent symptoms in those with B12 deficiency or insufficiency. Decreased appetite (p=0.003) and weight loss (p=0.010) were significantly associated with low B12 levels. Dietary patterns showed strong associations: reduced milk intake (72% deficient) and infrequent red meat consumption (49.6% deficient) were linked to deficiency. Vitamin D correlated positively with B12 levels (r=0.215, p=0.006), while mean corpuscular volume correlated negatively (r=-0.151, p=0.019). No significant associations were found with BMI (p=0.175), comorbidities (p>0.05), or metformin/PPI use (p>0.05).This study demonstrate that low vitamin B12 levels are strongly associated with inadequate consumption of milk and red meat, highlighting the central role of dietary insufficiency rather than chronic comorbidities or medication use. Constitutional symptoms—including decreased appetite and weight loss—alongside neurological manifestations such as numbness and weakness, were more prominent among deficient individuals, reinforcing their value as clinical indicators. The positive correlation between vitamin D and B12 levels suggests shared nutritional and socioeconomic determinants affecting overall micronutrient status. The absence of significant associations with BMI, metformin, and PPI use indicates that diet and socioeconomic factors may be more influential in this setting.Low vitamin B12 levels were associated with specific dietary insufficiencies, constitutional and neurological symptoms, and hematological indices. These findings highlight the need for heightened clinical awareness and integration of dietary counseling within primary care. These findings highlight the need for targeted screening and interventions to prevent deficiency in underprivileged populations