Low defences: what's normal and when to see a doctor

What people call "low defences" is often just life happening: colds that pile up through the winter, a bad week of sleep, a stressful stretch. Colds really are very common — an adult catches two to three a year, a small child four or more — and more than 200 different viruses can cause them. "Low defences" is not a diagnosis either. What exists in medicine are immunodeficiencies, identified by a doctor using specific tests, and those are a different matter entirely.

The question worth asking is this: is the pattern you are living the normal pattern of someone exposed to a lot of viruses, or is it a signal that you are worth assessing? There are things you can change this week, with reasonable evidence behind them, and there are a handful of signs that justify an appointment. The rest of this piece is about that distinction.

What usually explains infections that keep coming back

Before you think about supplements or "boosting" your immune system, it is worth looking at what sits around it. A recent review from Harvard Health Publishing is honest on this point: the idea of "boosting" immunity makes little scientific sense, and there are no proven direct links between lifestyle and improved immune function. What there is, the same source says, is common sense — healthy habits probably help immune function and bring other well-demonstrated benefits along with them.

Put another way: there is no button to press. There are factors that the evidence associates with greater susceptibility to infection, such as lack of sleep. The most common ones are tedious to list.

• Short sleep. In an experimental study of 164 healthy adults exposed to a rhinovirus, those sleeping less than 5 hours a night were clearly more likely to develop a clinical cold than those sleeping more than 7. The same held for people sleeping between 5 and 6 hours. The authors concluded that sleeping less was associated with greater susceptibility to the common cold.
• A diet poor in fruit and vegetables, and too much alcohol. Both feature in healthy-lifestyle recommendations.
• Smoking. It is on the list of things to avoid, with no nuances.
• Prolonged stress, which the same list recommends trying to minimise.
• Exposure. That one is not a personal failing.

There are also causes that do not depend on lifestyle at all. MedlinePlus notes that the immune response may be reduced by inherited conditions, by medicines that weaken the immune system (such as corticosteroids and chemotherapy), by conditions such as HIV/AIDS, by malnutrition and by ageing, since the immune system becomes less effective with age. All of these are identified in a consultation.

What you can change this week

Start with what has the most support. Harvard Health Publishing lists a set of healthy-lifestyle strategies: not smoking, eating a diet rich in fruit and vegetables, exercising regularly, keeping a healthy weight, drinking alcohol in moderation, sleeping enough, taking steps to avoid infection (washing your hands often), trying to minimise stress, and keeping recommended vaccinations up to date.

Little of that is new. The problem is that "sleeping enough" is not a useful instruction. Be concrete with yourself: how many nights in the past week did you sleep less than seven hours? If the answer is most of them, that is where to start. You do not need a life overhaul — you need to protect your bedtime for two or three weeks and see what happens.

Frequent handwashing sounds trivial and is not. With more than 200 viruses capable of causing a cold, reducing exposure remains a sensible measure. The same applies to washing your hands often, something health authorities include among the ways to avoid infections.

As for exercise, food and alcohol, the logic is identical: small corrections held for weeks are worth more than one perfect week followed by a slide back to the same old thing. And with recommended vaccines — do not invent your own list, confirm with your doctor or pharmacist which ones apply to you.

One thing the available evidence does not let us promise: that any of these changes will guarantee you fewer infections this winter. What can be said is that they make sense for several reasons at once, and that some of them have studies behind them pointing to an association with fewer colds.

What probably will not help you

Here it is worth pushing back on some popular wisdom. The same Harvard Health Publishing review notes that there is some experimental evidence that micronutrient deficiencies — in zinc, selenium, iron, copper, folic acid and vitamins A, B6, C and E — alter cellular immune responses. But it adds that it is not known whether this translates into changes in the human immune system that affect health, and that taking megadoses of a single vitamin does not help. The phrase used is blunt: more is not necessarily better.

That cuts a lot away. It cuts the idea that taking high doses of vitamin C in the week you feel a cold coming on will sort anything out. It cuts the logic of stacking several supplements: Harvard Health Publishing states that taking megadoses of a single vitamin does not help, and that more is not necessarily better. And above all it cuts the idea that there is a correct dose for "raising your defences".

It is also not worth diagnosing yourself on the basis of vague symptoms. The signs that lead a doctor to suspect an immunodeficiency are infections that return or will not clear, or a serious infection caused by germs that do not usually cause serious infection. And the anxiety around the topic — reading everything, changing everything, buying everything — is itself a source of stress nobody needs.

Where supplements honestly fit

They fit in a small, specific place. The available evidence on micronutrients and immunity is early and does not allow anyone to claim that taking a supplement with vitamin C, vitamin D3 or zinc will protect you from colds. What is known is that deficiencies in these nutrients alter immune responses in experimental settings — which is different from saying that people who are not deficient benefit from taking more.

That is why the right question is not "which supplement should I take?" but "might I be lacking something?". Even so, there is no scientific proof of a direct link between lifestyle and strengthened immune function. If you are unsure, a doctor or pharmacist can help you work out whether anything is worth assessing before you buy bottles.

If, after all that, you want to add a supplement to your routine, TuttiBear has Immunity & Defense Gummies with Echinacea, for adults, at two gummies a day. Each serving provides echinacea extract, vitamin C, zinc, vitamin D3, selenium and Lactobacillus rhamnosus. We are not promising it will protect you from anything — no supplement does that — and the pack says the essential part: food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Contains polyols. Excessive consumption may produce laxative effects. If pregnant, breastfeeding, suffering from a medical condition or taking medication, consult a healthcare professional before use. If you are looking for winter solutions, start with your sleep hours.

The signs that mean book an appointment

Here the line is clear, and it is worth separating it from what is normal. Two or three colds a year is normal. A cold that will not shift has its own rules too: the NHS advises seeing a doctor if symptoms get worse or have not improved after 10 days, if you have a high temperature for more than 3 days, if you have a cough for more than 3 weeks, or if symptoms appear in someone with a long-term condition or a weakened immune system.

There is another set of signs, more structural, that MedlinePlus associates with suspected immunodeficiency: infections that return repeatedly or do not clear, a serious infection caused by germs that do not usually cause serious illness, a poor response to treatment for infections, and a slow or incomplete recovery from an illness. If you recognise your pattern of the last few months here, it is not a reason to panic — it is a reason to book an appointment. Diagnosis is done with medical tests, such as immunoglobulin levels in the blood and white cell counts. It is not done at home and it is not done with a questionnaire on the internet.

Note that none of these signs is there for you to self-diagnose with. They are there to help you decide whether it is worth talking to someone. That is the only honest use of a list like this.

How long before you can tell whether it is working

We do not have an exact timeframe to give you, and be suspicious of anyone who does. What can be said precisely is that it is not established that habit changes directly strengthen immunity, although they make sense for their general health benefits. If you sleep better, do not expect a measurable transformation, because it is not established that habit changes directly strengthen immunity. What it does make sense to expect are the general health benefits associated with healthy lifestyle habits: not smoking, eating a diet rich in fruit and vegetables, exercising regularly, keeping a healthy weight, drinking alcohol in moderation, sleeping enough, washing your hands often, minimising stress and keeping vaccinations up to date.

If what worries you is a pattern of infections that has dragged on for months, the relevant deadline is not the habits one — it is the appointment. Booking a conversation with your doctor or pharmacist is the only thing in this piece that can give you a concrete answer about your own case. Everything else is what is known in general, applied with common sense to what we do not yet know about you in particular.