The Diseases of Ageing
Without a doubt, modern medicine has been able to keep us alive for longer. At the turn of the twentieth century, life expectancy at birth globally was only 32 years. Just one hundred years later, that figure had risen to 67 years, and today it is higher still at 73 years, after a small dip during the Covid-19 pandemic, which disproportionately affected the elderly. In Hong Kong, the place I call home, life expectancy at birth is 85.77 years, the highest in the world, narrowly beating out Japan and South Korea. By sex, this breaks down to 83.10 years for men and 88.39 years for women.
As a consequence of living longer lives, there is an increase in the number of age-related diseases, aptly referred to as the disease of ageing. Every day, there are around 170,000 deaths around the world on average. Of these, it is estimated that 70-80% are attributable to the diseases of ageing, depending on the country/region.
By diseases of ageing, I am referring to the following:
Cardiovascular disease;
Cancer, with the deadliest being lung cancer, accounting for just under 20% of all cancer deaths worldwide;
Insulin resistance and type 2 diabetes;
Respiratory diseases, such as Chronic Obstructive Pulmonary Disease (COPD) and lower respiratory infections, such as pneumonia;
Neurodegenerative diseases, around two-thirds of which are Alzheimer’s disease;
Musculoskeletal disorders, including osteoporosis, osteoarthritis and sarcopenia;
Age-related macular degeneration (AMD);
Chronic kidney disease (CKD);
Liver cirrhosis and fatty liver disease.
Of these diseases, I call the top five The Deadly Quintet, which are responsible for the most deaths. In fact, an estimated 80% of all deaths of over 50s are associated with one or more of The Deadly Quintet. In a world with a rapidly ageing population, The Deadly Quintet is especially pertinent.
The Role of Metabolic Syndrome
The diseases of ageing often take many years to develop. Sometimes the body gives early warning signs; other times the warning signs are too late, such as the case with a myocardial infarction (a heart attack). A heart attack is usually very sudden, with no prior warning to the sufferer that he has cardiovascular disease, more specifically atherosclerosis. If the person is fortunate enough to survive the event, it can serve as a wake-up call to take action to prevent the disease from progressing (by taking medication and adopting healthier lifestyle habits), but by then, the damage to the heart muscle has already been done.
However, cardiovascular disease takes many years to develop, similarly for the other four diseases of The Deadly Quintet. In many cases, the precursor to these diseases is a broader condition known as Metabolic Syndrome. In very general terms, this condition develops when the body starts to have problems regulating itself. Although there are cases of metabolic syndrome that are genetic, it is almost always a lifestyle disease, meaning that we can do something to prevent it.
Metabolic syndrome is a silent disease because it progresses very slowly over many years, initially with no symptoms. It describes a cluster of interrelated cardiometabolic conditions that, if left unchecked, will progress to cardiovascular disease, type 2 diabetes, neurodegenerative diseases and even some cancers.
One of the key signs of metabolic syndrome is insulin resistance. Insulin is an important signalling hormone for which every cell in the body has a receptor. Insulin’s most famous action is controlling blood glucose levels, whereby the insulin receptor allows glucose to exit from the blood and enter into the cells, where it is stored in the form of glycogen.
Unfortunately, there is no easy way to accurately measure insulin levels in the body outside laboratory conditions. Most common techniques measure blood glucose levels as a proxy, but that is not the same thing. Insulin levels can remain high in the body, even after blood glucose levels fall.
There is a more accessible test for measuring insulin resistance called HOMA-IR (Homeostatic Model Assessment for Insulin Resistance). This test estimates insulin resistance using a simple blood test based on fasting levels of both plasma glucose and insulin.
Another way to determine whether a person likely has metabolic syndrome is to see if at least 3 of the following 5 conditions are met:
Increased waist circumference - over 94cm (37in) for men and over 80cm (31.5in) for women;
Elevated serum triglycerides (>150 mg/dL);
Reduced high-density lipoprotein (HDL) cholesterol (<40 mg/dL in men and <50 mg/dL in women) or currently taking medication for dyslipidaemia;
Elevated blood pressure (>130/85 mm Hg); and
Elevated fasting serum glucose (>100 mg/dL) or currently taking glucose-lowering medication.
Treating metabolic syndrome can be considered as an upstream intervention to prevent the development of The Deadly Quintet. It is one of the most overlooked low-hanging fruit, as it is treatable with some basic lifestyle interventions, and would significantly improve healthspans across populations. Treating insulin resistance will in many cases also treat metabolic syndrome.
What is Insulin Resistance?
Insulin resistance develops because too much glucose enters the bloodstream without anywhere for it to go. In a healthy person, carbohydrates from a meal are converted into glucose and released into the bloodstream. In response, the body releases insulin, which acts like a key, unlocking the skeletal muscle cells to allow them to absorb the glucose in the form of glycogen. Muscle cells account for over 80% of the post-prandial glucose uptake. Once the skeletal muscle cells are saturated with glycogen, excess glucose is diverted to the liver where it is stored, also as glycogen.
Insulin resistance starts to develop when both the skeletal muscles and the liver are already saturated with glycogen and additional glucose enters the bloodstream post-prandially. There is nowhere for this glucose to go, and if it stays in the blood for too long, it causes serious harm to nearly every organ system, especially blood vessels, nerves, kidneys, eyes and brain. So, in an effort to clear the glucose from the bloodstream, the body releases more insulin to increase the signalling, and the body reacts by freeing up storage space in the liver. It does this by converting the stored liver glycogen into fat through a process called de novo lipogenesis.
Simple Tips for Avoiding / Reversing Metabolic Syndrome
Metabolic syndrome is one of the fastest-growing diseases globally and is particularly linked to sedentary lifestyles and to eating ultra-processed, energy-dense foods.
The best way to avoid metabolic syndrome, or even reverse it, is to adopt these five lifestyle habits:
Be physically active - we are physical beings that evolved to always be on the move, which is why our bodies are struggling to cope with the modern, sedentary lifestyle in which we spend hours on end seated, staring at screens;
Consume no more calories than you burn in a day;
Build muscle - skeletal muscle acts like a sponge for glucose; the more skeletal muscle you have, the more glucose you can absorb from the bloodstream;
Incorporate plenty of fibre into your diet, consuming it at the start of a meal buffers the release of glucose into the bloodstream;
Take a 15-minute walk after a meal - this helps bring down both insulin and glucose levels post-prandially.