Immunity, and what can and cannot be boosted

The concept of boosting immunity is commercially useful and biologically incoherent, since an immune system operating at higher intensity is what autoimmune disease and allergy consist of.

How it actually works

Two arms working together.

Innate immunity provides immediate, non-specific defence: barriers, inflammatory responses and cells that respond to broad patterns.

Adaptive immunity develops specific responses to particular pathogens, involving T and B cells, and retains memory — which is the basis of both recovering from an infection and of vaccination.

The system is regulated rather than scalable, and the goal is appropriate response rather than more response.

The one intervention that genuinely does what people want

Vaccination, which trains adaptive immunity against a specific threat without the disease.

It is the only widely available intervention that reliably and specifically improves immune protection.

Which is worth stating plainly given that the same market selling immune supplements frequently discourages the intervention that works.

Adult vaccination is under-used: influenza annually for eligible groups, pneumococcal, shingles at the recommended age, tetanus boosters, COVID-19 according to current guidance, and travel vaccinations.

What genuinely affects immune function

Supported by evidence, and none of it is sold.

Sleep. Experimental restriction reduces antibody response to vaccination, and prospective studies have found shorter sleep associated with higher rates of respiratory infection after controlled exposure.

This is among the most robust findings in the area.

Chronic stress, which is associated with impaired wound healing, reduced vaccine response and increased susceptibility to infection in controlled studies.

Nutrition, where deficiency impairs function — protein-energy malnutrition, zinc, vitamin A, vitamin D and others — and where correcting deficiency helps while supplementing a replete person does not.

Physical activity, where moderate regular activity is associated with lower infection rates, and where very heavy training loads have been associated with the opposite in athletes.

Smoking and excess alcohol, both of which impair defences measurably.

Obesity, which is associated with altered immune function and worse outcomes in several infections.

Age, which brings immunosenescence — a real decline in function — and which is why vaccination schedules differ for older adults.

What is sold and does not work as claimed

Vitamin C, where large reviews find that routine supplementation does not prevent colds in the general population, with a small reduction in duration and some benefit in people under extreme physical stress.

Echinacea, where evidence is inconsistent.

Zinc, which has some evidence for reducing cold duration if started very early and at adequate dose, with side effects that limit its use.

Most mushroom, herbal and proprietary immune formulations, where evidence is thin.

Elderberry, where there are small studies and a theoretical concern raised about immune activation in specific circumstances.

And anything claiming to boost immunity generally, which is not a coherent target.

Hygiene, in proportion

What reduces transmission.

Hand hygiene, which has good evidence for reducing respiratory and gastrointestinal infection.

Staying away from others when infectious, which is a workplace culture issue as much as a personal one.

Ventilation, which received deserved attention recently and which matters for airborne transmission.

Respiratory etiquette.

Food hygiene, discussed elsewhere on this site.

And appropriate use of antibiotics, since they do not treat viral infections and since resistance is a collective problem created by individual prescriptions.

The hygiene hypothesis

Frequently misapplied.

The observation that reduced early microbial exposure is associated with higher rates of allergic and autoimmune disease is well established.

It concerns the diversity of environmental microbial exposure in early life, particularly in relation to farms, animals, siblings and the microbiome.

It is not an argument against handwashing or vaccination, which is how it is routinely deployed.

When immune function is genuinely a concern

Patterns warranting assessment rather than supplements.

Unusually frequent, severe or persistent infections.

Infections with unusual organisms.

Poor response to standard treatment.

Recurrent deep abscesses or unusual sites.

Failure to thrive in children with recurrent infection.

And immunosuppression from medication or disease, where specific precautions and vaccination schedules apply and where advice should come from the treating team.

General information only, not medical advice. Consult a qualified clinician about recurrent infections and about which vaccinations apply to you.