The pandemic has renewed attention to the link between an individual’s general health and their susceptibility to serious health complications from contracting respiratory illness – with the factor of obesity particularly coming into the frame.
Obesity’s adverse effect on an array of diseases – including diabetes, cardiovascular disease and cancer – is now well-established. However, obesity’s impact on the immune system, the body’s first line of defence against infectious diseases, is not understood quite as thoroughly.
What does research tell us about lifestyle’s effect on immunity?
We are all familiar with the phrase “an apple a day keeps the doctor away”, and it’s a mantra borne out by science. According to studies mentioned by the non-profit Obesity Action Coalition, high intakes of fibre, protein and antioxidants bode well for proper functioning of the immune system.
Consuming too little protein runs the risk of protein-energy malnutrition, which has been linked with significantly impaired immunity. Meanwhile, studies suggest that exercising can lead certain immune cells to proliferate and consequently help to strengthen the immune system.
Is it possible to isolate obesity as a risk factor for immunity?
Yes, as an obese person who exercises regularly and maintains a healthy diet can remain vulnerable to decreased immune function. Research indicates that obesity itself is capable of hampering immunity through, for example, reducing macrophage and dendritic cell function.
You might notice the word “macrophages” popping up often in discussions about obesity’s influence on immunity, as the word refers to immune cells which invade fat tissue and, there, interfere with the immune system’s ability to defend itself against viral infection.
Scientists say this situation can brew up a “cytokine storm”, where the immune system is overwhelmed in a manner resulting in inflammation, serious harm and potentially even death.
Macrophages are drawn to a particular kind of fat tissue of which people from black, African and ethnic minority backgrounds (BAME) have especially high concentrations. This could help to explain why people in the BAME bracket “have elevated rates of diabetes, and may be more vulnerable to the virus,” Dr Dyan Sellayah of the University of Reading explained to BBC News.
Could a weak immune system be held responsible for obesity?
While there isn’t (yet) a simple, clear-cut answer to this question, research findings suggest this could indeed be the case. In a 2015 study, researchers found that mice lacking a specific type of immune cell became obese and showed increases in their blood pressure and cholesterol.
While inflammation – a heightened immune response – was already correlated with obesity, it has been tricky for scientists to decipher whether inflammation leads to weight gain or is instead simply a side effect of weight gain, given that fat cells are capable of producing inflammatory molecules.
In a study led by immunologist Yair Reisner of the Weizmann Institute of Science based in Rehovot, Israel, researchers engineered mice to remove dendritic cells wielding an immune molecule called perforin, which was already known to kill diseased cells in the body. Reisner told Science that his team “found that the mice gained weight and developed metabolic syndrome.” Yale School of Medicine immunologist Vishwa Deep Dixit, who did not participate in the study, claimed that it “definitely moves the field forward,” adding: “The data seems really solid.”
Issues with immune health, then, have not always been easy to connect back to obesity, with the latter’s role as a cause or consequence uncertain in many studies.
Nonetheless, one thing does seem clear from the research undertaken so far: obesity often occurs alongside compromised immune function. The onus is therefore on all of us to pursue the healthiest possible lifestyles to help combat the many potential ill effects of both