Introduction
Five years since the World Health Organization declared the Covid-19 pandemic, scientists are gaining a clearer understanding of how the virus can leave lasting effects on the body long after the initial infection has passed. While some of Covid’s immediate effects were apparent early on—such as its potential to cause severe illness and death, particularly in those with pre-existing conditions like diabetes and heart disease—the long-term consequences of the virus have taken years to unpack. Research has revealed that Covid can lead to persistent, sometimes invisible changes in various parts of the body. These changes, often referred to as long Covid, can include symptoms like chronic fatigue and brain fog that persist for months or even years. However, long Covid encompasses more than just these symptoms; it also includes lung and heart damage and changes to the gut microbiome that may not always be directly associated with long Covid but can still have a profound impact on overall health.
The Lungs
Covid-19 can cause long-term lung damage, leading to symptoms such as persistent shortness of breath and coughing. In rare cases, the virus can result in complications like pneumonia, scarring, and the development of small masses of tissue called nodules in the lungs. These scars can make breathing more difficult. According to small studies, over 10% of people hospitalized with Covid had lung scarring and other issues two years after their infection. The virus invades cells along the airways, causing inflammation that can damage or destroy healthy lung tissue. This can impair the lungs’ ability to deliver oxygen throughout the body. As the lungs attempt to heal, they form scar tissue, which can stiffen the lungs and reduce their capacity, leading to lasting symptoms like coughing and shortness of breath.
The Gut
Covid-19 can also cause chronic gastrointestinal problems, such as reflux, constipation, diarrhea, and abdominal pain, which can last for months or even years. A 2024 study estimated that as many as 10% of people experienced lasting abdominal pain and 13% had gastrointestinal issues a year after their infection. While the exact reason for Covid’s impact on gut function is not yet fully understood, research suggests that the virus disrupts the gut microbiome, reducing the number of beneficial microbes and increasing harmful ones. “Good” microbes help reduce inflammation, while “bad” ones can increase it. Inflammation from the infection and altered gut microbes can harm the lining of the intestine, allowing toxins and undigested food particles to escape into other tissues. This can trigger immune responses, leading to food intolerances. Inflammation may also damage the nerves that control gut contractions and pain signals, causing symptoms like diarrhea or constipation.
The Brain
Covid-19 can leave a lasting impact on the brain, with symptoms such as headaches, dizziness, confusion, difficulty concentrating, and memory gaps persisting long after the initial infection. Studies have found that 20 to 30% of people infected with Covid experienced brain fog at least three months after their infection. Additionally, Covid can lead to conditions like anxiety or depression or exacerbate existing mental health issues. Persistent inflammation is a key factor in these neurological effects, as it can damage neurons and disrupt connections between synapses. Brain areas involved in cognition and emotion may be particularly vulnerable to inflammation, which could explain why Covid can induce or worsen mental health issues. Another theory is that the virus disrupts the blood-brain barrier, which protects brain tissue and supports cognitive function. Fragments of the virus may also linger in the brain long-term, contributing to ongoing cognitive symptoms.
The Heart
A Covid-19 infection can increase the risk of heart problems, including heart attacks, strokes, heart muscle damage, and irregular heartbeats. One large study found that having Covid doubled the risk of a major cardiovascular event for up to three years. During an acute infection, fever and inflammation can place extra strain on the heart, particularly in individuals with pre-existing conditions like artery plaque buildup or stiffening heart muscle. In such cases, the increased demand on the heart can lead to irregular heartbeats or heart attacks. More commonly, scientists believe that the virus causes inflammation that injures the heart muscle and damages blood vessel linings, leading to inflammation and blood clot formation. This can result in blockages that cause heart attacks or damage to heart muscles and tissues, potentially leading to heart failure or arrhythmias. People hospitalized for Covid are at the highest risk of both short- and long-term heart complications. Research suggests that individuals with non-O blood types (A, B, or AB) may have a higher risk of heart issues, possibly due to how their blood clots.
The Circulatory System
Studies of long Covid patients have revealed that their bodies often struggle to circulate blood effectively, particularly moving blood from the legs and abdomen back to the heart. This can reduce the heart’s pumping capacity, leading to fatigue, shortness of breath, and a general feeling of unwellness after exercise. The exact cause of these circulatory issues is unclear, but scientists hypothesize that inflammation may damage the nerve fibers that regulate blood vessel contractions. This can impair blood flow, according to Dr. David Systrom, a pulmonary and critical care physician at Brigham and Women’s Hospital. Additionally, in some long Covid patients, muscles may be less efficient at extracting oxygen from the blood, making it harder to exercise. The mitochondria, the energy-producing structures within cells, may also function improperly, further impairing muscle tissue and contributing to the overall struggle with physical activity.
Conclusion
The long-term effects of Covid-19 are complex and far-reaching, affecting multiple systems in the body. Inflammation plays a central role in many of these effects, damaging tissues and disrupting normal bodily functions. While most people recover fully from Covid-19, millions worldwide are grappling with the lingering consequences of the virus. By understanding these effects, scientists and healthcare providers can better diagnose, treat, and manage long Covid, helping patients recover and regain their quality of life. Continued research is essential to uncover the full extent of Covid’s impact and to develop effective strategies for mitigating its long-term consequences.