Why everything you thought you knew about your immune system is wrong

You’ve likely heard that taking vitamin C can prevent a cold, or perhaps TikTok has led you to try turmeric or some other supplement to enhance your immune system. The truth is, these sweeping claims are mostly unfounded. There’s a plethora of myths surrounding immunity, as pointed out by Daniel Davis, an immunologist at Imperial College London.

In his latest book, Self Defence: A myth-busting guide to immune health, he sets out to debunk these widespread misconceptions. Davis illustrates that with every technological advancement, like using super-resolution microscopy to examine the interactions of immune cells with their targets, the astonishing complexity of the immune system becomes increasingly evident.

However, rather than leaving us feeling helpless, he shares with New Scientist that this complexity is liberating—it enhances our understanding of the immune system’s role in mental health, informs us about lifestyle factors that may detrimental to our immunity, and helps us better discern facts from fads.

Helen Thomson: Let’s begin with the term “immune health” and the idea that we can enhance it. That mindset isn’t entirely accurate, correct? 

Daniel Davis: Absolutely, there are countless products claiming they can “boost” your immunity. This notion seems misleading since, while it’s essential to have a strong immune system to combat infections, simply ramping up its power may lead it to attack the body’s own healthy cells, resulting in autoimmune diseases or allergies. It must function in a balanced manner to respond appropriately to threats. 

So, is the goal to cultivate a “smarter” immune system?

Expressions regarding immune health often lack the necessary nuance. Everyone’s immune system is incredibly unique; genetically speaking, it’s what sets you apart the most. When discussing immune health, we can only reference factors that have shown to benefit people on average, but determining whether a specific factor will aid you individually is quite challenging. 

One major insight is that the immune system is not an isolated entity; it is shaped by diet, exercise, and our microbiome. Can we identify which lifestyle factor significantly influences immune health?

The evidence clearly indicates that chronic stress has the most significant impact on our immune health. There’s substantial evidence regarding other factors, but establishing direct causation remains tricky. In the case of stress, however, we possess a molecular understanding of its effects. 

And what happens during this process?

When your body perceives a threat, it triggers the fight-or-flight response—signals traveling from your hypothalamus to your pituitary and adrenal glands produce stress hormones, namely adrenaline and cortisol, to prepare your body for action. This response temporarily suppresses immune system activity. This is acceptable in brief bursts, like after a parachute jump. After such an event, immune cell counts return to normal in about an hour. But when someone experiences chronic stress, elevated cortisol levels persist, which can weaken the immune system over time, creating significant issues. 

Our confidence in this conclusion is bolstered by lab experiments where considering the efficacy of your immune cells in targeting virus-infected cells or cancer cells demonstrated that the introduction of cortisol diminishes their effectiveness. In conjunction with observations that individuals under prolonged stress respond poorly to vaccines and have higher susceptibility to infections, we can assert that long-term stress indeed harms immune function. 

If I undergo stress and make lifestyle adjustments, can I measure my immunity to determine if it’s beneficial? 

Proving that reducing long-term stress translates to improved immune health remains an elusive task. Theoretically, it seems plausible, but demonstrating concrete results is complex. In clinical settings, the count of white blood cells is often used as a proxy for assessing immune health, but given the variety of immune cells present in the body, and the fact that every single cell contributes to this system, identifying a straightforward indicator can be challenging. 

I’ve heard reputable scientists on social media claiming specific actions to boost immunity. Should we take these claims seriously? 

Take orange juice, for instance. Growing up, I believed that drinking orange juice would ward off a cold without questioning it. Yet, the reality is this is misleading. The narrative traces back to Linus Pauling, a two-time Nobel laureate, who became a cultural figure in the 1970s with his book Vitamin C and the Common Cold, which rapidly became a bestseller. Manufacturing facilities sprang up to meet the skyrocketing demand for vitamin C, yet his assertions were based on selective data and anecdotal experiences, heavily promoted by media outlets. 

The reality is that high doses of vitamin C show no significant effect on preventing colds. Research indicates that while high supplementation may shorten the duration of colds by approximately 8%, interpreting this data is complex, as individuals taking these doses likely engage in other healthful behaviors. Ultimately, this myth deep-rooted in our culture stems from one notable scientist who passionately advocated a compelling yet fundamentally flawed idea.

Reflecting on contemporary claims, we need to approach the proclamations of any single expert with caution. While expert opinions are valuable, scientific consensus is the reliable path forward. 

Interest is growing in the connections between our immune system, inflammation, and mental health—this is indeed a captivating area. 

The relationship between the immune system and mental health presents an exciting frontier. Researchers have noted that individuals taking anti-inflammatory medications for rheumatoid arthritis reported improvements in their mental well-being before their physical symptoms improved. These medications act by inhibiting cytokines—protein molecules secreted by immune cells to communicate with each other. 

Another line of inquiry shows that certain mental health conditions correlate with elevated inflammatory markers in the bloodstream. A study on children with high IL-6 levels revealed that these individuals were more prone to depression by age 18.

Perhaps the weightiest evidence comes from animal studies: when animals are injected with IL-6, they exhibit withdrawal behaviors, similar to conditions of poor mental health, characterized by reduced exploration and social interaction. 

However, actionable strategies derived from this understanding remain sparse. Research has shown that using over-the-counter anti-inflammatory medications such as aspirin or ibuprofen does not alleviate depression symptoms. Additionally, trials conducted on administering cytokine inhibitors to people without rheumatoid arthritis have yielded either negative or inconclusive outcomes. 

Future investigations must focus on designing assessments capable of identifying individuals who may garner benefits—could it be that those with certain mental health disorders and elevated cytokine levels in their blood, possibly alongside yet-to-be-discovered biomarkers, may respond favorably to anti-cytokine therapies? We are currently in the dark about this. However, understanding that various mental health challenges could correlate with aspects of immune function could offer significant insights—this represents a vital area of research. 

When people ask you for a definitive action they can take to enhance their immunity, what do you typically suggest? 

There are indeed certain recommendations, but they are rarely straightforward. Chronic stress is undeniably problematic. Prioritizing adequate sleep is pivotal. Yet what qualifies as adequate sleep varies individually, and pinpointing a specific required amount is complex. The role of the microbiome is critical, but I cannot provide you with a guaranteed method to improve it. These responses may seem frustrating, but the key takeaway is the inherent complexity of this subject. Studying the immune system reveals a wondrous intricacy.