Recurring Infections

Infections that keep returning — repeated colds, sinus infections, urinary infections, or skin infections — beyond what circumstances explain. Most reflect exposure and habits rather than immune failure, but a genuine pattern warrants checking for the common, correctable causes: vitamin D deficiency, iron deficiency, diabetes, and poor sleep.

Evidence synthesis: Sleep is the most modifiable immune lever — a landmark study found adults sleeping under 6 hours were over 4x more likely to catch a cold after viral exposure than those sleeping 7+. Vitamin D supplementation has meta-analytic evidence (Martineau et al., individual-patient data across 25 RCTs) showing reduced respiratory infections, with the strongest effect in people who were deficient. Iron deficiency impairs immune cell function and is a common, testable cause, particularly in menstruating women. Undiagnosed or poorly controlled diabetes elevates infection risk measurably — recurrent skin or urinary infections are a classic first presentation. Smoking and chronic alcohol use impair respiratory and systemic immunity. True primary immune deficiencies are rare but are flagged by specific patterns: recurrent pneumonia, unusual organisms, or infections requiring IV antibiotics.