Frequent Infections

"Getting sick all the time" is one of the most common reasons people reach for immune supplements, and one of the least precisely defined. The first useful step is to establish what normal looks like. Healthy adults have two to three upper respiratory infections a year; parents of young children and teachers reliably have more, because exposure dominates. Children in daycare may have six to twelve a year and still be entirely normal. What raises concern is not frequency alone but pattern. Infections that need antibiotics repeatedly, that recur at the same anatomical site, that fail to clear, or that involve unusual organisms point toward something structural or immunological rather than bad luck. So does a history of two or more episodes of pneumonia, persistent oral thrush in an adult, or deep abscesses. For the far larger group whose immune system is intact, the drivers are mundane and modifiable. Short sleep is the best-documented: restricting sleep to four or five hours has been shown experimentally to roughly triple the odds of developing a cold after controlled rhinovirus exposure. Chronic psychological stress produces a similar effect through sustained cortisol elevation. Nutrient status matters at the margins — vitamin D deficiency, zinc deficiency and low protein intake all impair aspects of immune function, though correcting them helps only if they were low to begin with. Age matters too. Immune function declines gradually from middle age, a process called immunosenescence, which is why vaccination and nutritional adequacy become more important later in life.

• •More than four to six respiratory infections a year in an adult
• •Infections that take longer than two weeks to clear
• •Repeated need for antibiotics
• •Recurrent sinusitis, bronchitis or ear infections
• •Persistent or recurring oral or genital thrush
• •Slow wound healing
• •Fatigue that lingers well after the infection resolves
• •Swollen lymph nodes that persist

• •High exposure — young children at home, teaching, healthcare, public transport
• •Chronic sleep restriction below six hours
• •Sustained psychological stress
• •Vitamin D deficiency
• •Zinc deficiency
• •Inadequate protein intake or undernutrition
• •Poorly controlled diabetes
• •Smoking and vaping, which impair mucociliary clearance
• •Immunosuppressive medication including corticosteroids and biologics
• •Primary or secondary immunodeficiency
• •Allergic rhinitis mistaken for recurrent infection

Most frequent infection in otherwise healthy adults is a behavioural and exposure problem wearing an immunological costume. Sleep is the largest single lever: the Cohen rhinovirus challenge studies found that people sleeping under six hours were far more likely to develop symptomatic infection than those sleeping seven or more, after controlled viral exposure. Chronic stress acts through the same final pathway, with sustained glucocorticoid signalling reducing lymphocyte proliferation and antibody response. Nutrient deficiencies work permissively rather than causally. Vitamin D and zinc are both required for normal innate and adaptive responses, but supplementing above adequacy adds nothing — which is why immune supplements disappoint people who were never deficient. A smaller group has a genuine cause: uncontrolled diabetes, immunosuppressive treatment, HIV, haematological malignancy, or a primary immunodeficiency such as common variable immunodeficiency, which frequently goes undiagnosed into adulthood. The warning signs are severity and site-specificity, not simply count.