When 106-year-old Connie Titchen was clapped out of Birmingham City Hospital in mid-April, having survived her bout of coronavirus, she gave hope to silver seniors everywhere.

From the start of the crisis, increasing age has been associated with lower rates of beating the disease. But here was Connie, who had outlasted the Spanish flu and now seen off Covid-19, thanks – her family said – to her active and healthy lifestyle.

Yet, according to the Department of Health, anyone over 70 (let alone 100) is at higher risk of being vulnerable to the effects of Covid-19, with Boris Johnson, the Prime Minister, saying in March that over-70s should brace for 12 weeks indoors. NHS guidance puts all over-70s, regardless of medical condition, into the “clinically vulnerable” category.

However, some experts are querying whether using age as a matrix – and the cut-off point of 70 in particular – is a good idea. Might we be better off, they ask, looking at other contributory factors, such as weight, when it comes to shielding a specific population?

After all, a 70-year-old who plays tennis twice a week, doesn’t smoke or drink much alcohol, and whose Body Mass Index (BMI) – the NHS-approved metric that establishes if you are a healthy weight – is in the normal range must surely be a better bet against Covid-19 than a 40-year-old who smokes, binge drinks, never exercises and is clinically obese?

American research at Brown University, Rhode Island, is already under way that shows patients with a BMI over 35 are more likely to go into intensive care, and those with a BMI over 30, when combined with a history of heart disease, are more likely to need ventilation as well.

Can you compare the numbers of those who die from Covid-19 by age and by risk of obesity directly? Not yet. But according to the Office for National Statistics, about 60 per cent of deaths up to April 17 were men (11,405 compared to 7,707 women).

Most of these are likely to have carried excess weight, as almost three quarters (73 per cent) of Covid-19 patients who go into critical care are overweight or obese, says the Intensive Care National Audit & Research Centre – although typically just over half of these will recover and leave intensive care.

What's the right BMI? 

So why would obesity matter? According to research at the University of Texas in Dallas, fat cells of patients with obesity or type-2 diabetes increase production of angiotensin-converting enzyme 2 (ACE2). These are the proteins which the new coronavirus latches on to in the body, especially in the lungs.

As a result, say the researchers, who have just published their work in the journal Obesity, anti-diabetic drugs called thiazolidinediones could be useful to slow down the progression and severity of the disease.

Those of us without type-2 diabetes or who aren’t considered obese (with BMIs of between 30 and 39.9) or even morbidly obese (over 40), shouldn’t relax. According to the World Obesity Federation, a high percentage of the world’s population who will contract coronavirus will have a BMI over 25. For scale, a woman who is 5ft 6in tall and weighs around 70kg would have a BMI of 25.

So could we be looking at BMI rather than age as the ultimate risk factor?

Philip Calder, professor of nutritional immunology at the University of Southampton, says the question is interesting.

“There isn’t enough data yet,” Prof Calder says, “but we know there are commonalities with ageing and obesity. In both cases, the immune system doesn’t work as well.”

He adds: “During the H1N1 [swine flu] pandemic, it was seen that obese people were at greater risk of developing severe influenza. And after that, we learnt that the obese don’t respond well to the flu vaccine.”

This may be due to low-grade inflammation, which is a factor of obesity – with some predisposed to excessive inflammation that in turn can cause lung damage.

He also points to where the virus has hit hardest: the UK, the US, western Europe – rather than developing countries in Africa or South America.

“There will be interesting data to come from America in time,” he says.

The underlying health risks

The idea that age matters more than a factor like BMI seems to go against the work done on longevity in recent times, too. Most of us have an innate sense of how well we are, says Sarah Harper, professor of gerontology at the University of Oxford: “The idea of a blanket rule saying that over-70s need to be locked away for their own good seems wrong.”

Prof Harper, who established Oxford’s Institute of Population Ageing, adds: “At a population level, we know that the risk of having severe symptoms or surviving the virus increases from the age of 60 onwards – but that is linked to underlying health risks including cardiovascular disease, high blood pressure, diabetes and obesity which come with age.”

And although the chances of getting co-morbidities or underlying conditions increase with age, Prof Harper explains: “Some of us are genetically programmed to age earlier or later than normal.

“But if you keep fit and active, you can delay the onset of serious disease.”

The idea that you can lower your biological age (if not your chronological one) by taking better physical care is one that has long appealed to Baroness Jenkin, who sits on the All-Party Parliamentary Group on Obesity.

“If we all live by the five rules of following a healthy diet,” says Baroness Jenkin, “[among other things] maintaining a healthy weight, not smoking, and taking daily exercise, we will be more able to fight off this disease if it comes for us regardless of age.”

And that is another way of taking pressure off the NHS, she points out. Which is something of importance when you consider that a second spike of the disease is almost inevitable.

“We could be using the time now to prepare our bodies for that by watching what we eat and keeping moving,” she says.

Lifestyle change

Using obesity (or other underlying health conditions) as a way to decide who stays quarantined longest might bring another public health benefit too: being warned that you need to stay in lockdown because of your weight might be the incentive some need to look hard at their lifestyle.

Just as there is evidence that more smokers are giving up – with a YouGov survey finding out that up to 300,000 Britons have quit smoking due to concerns over coronavirus – future research might find that a significant number of us successfully lost weight as a prophylactic against Covid-19.

So should we switch from shielding the elderly to the cuddly?

The virus is so new that we don’t have research that can definitively state which metric would work best, says Mauricio Avendano, professor of public policy and global health at King’s College London.

“We have picked age as an easy target,” says Prof Avendano, “but while it is important to protect older people, we don’t want to marginalise them.”

So where does that leave someone who takes statins for high cholesterol, say?

“Those with controlled high cholesterol or hypertension will have reduced risk of stroke or heart disease. One might expect them to have a reduced risk of any associated conditions,” such as Covid-19, “but we just don’t know yet. There are pathways we need to understand.”

The lack of definitive research means experts are urging caution.

Dr Partha Kar, a consultant in diabetes and endocrinology at Portsmouth Hospitals NHS, says it is possible in the future that age could be part of a shortlist of high-risk factors for the coronavirus alongside ethnicity, BMI and whether you have diabetes.

However, age alone is not a binary cut-off, says Dr Kar. “I’m not going to say to someone who is 80 and very fit not to leave the house. But if they were over 60 with high blood pressure and with an ethnic minority background, then my advice might be different.”

Dr Kar says that BMI measurements should be used with care: “Someone with a low BMI (below 20) would also be considered high risk if they got Covid-19 as they would also need special care.”

What is true for all, says Prof Calder, echoing Baroness Jenkin, is that we need to think about what we’re eating right now.

“It’s important to have a healthy diet,” he says, “as that way we can keep up our immune defences.” And that’s regardless of however the numbers stack up.

Expert advice to stay fit in the pandemic