For over two decades, Mr Edward Lee, 62, has been living with hypertension - a chronic disease that now makes him more vulnerable to experiencing severe symptoms from the coronavirus.

It is a risk faced by nearly one in four adults between the ages of 39 and 60, and more than half of those aged 60 to 69, according to the Ministry of Health.

The Singapore Heart Foundation (SHF) has warned that patients with hypertension "are more likely to develop severe symptoms and are at higher risk of complications from Covid-19". This is regardless of age, it states on its website.

Its chairman, Professor Tan Huay Cheem, said about 20 per cent of Covid-19 patients in Singapore had pre-existing hypertension.

Among the 23 deaths so far, 10 patients aged between 60 and 86 were reported to have a history of hypertension.

While Mr Lee is aware of this, he does not worry as he takes personal hygiene seriously.

"I wash my hands with soap frequently and wear a mask outdoors. I trust that I have followed the best guidelines," said the manager in a beverage company, although he conceded that there is still a possibility of getting infected.

Given the prevalence of hypertension, it is not surprising that the disease is common among patients with Covid-19, said Prof Tan, who is also director of the National University Heart Centre.

He said it is especially important for those with hypertension to maintain normal blood pressure during this time.

Hypertension can result in complications such as coronary artery disease, heart failure, chronic kidney failure, abnormal heart rhythms and stroke, which can worsen the general health and immunity of Covid-19 patients, especially the elderly, he said.

"The presence of such complications increases the disease and death risks of Covid-19 patients who also suffer from hypertension," said Prof Tan.

Blood pressure is also a vital parameter in managing the health of Covid-19 patients, particularly in the intensive care unit, he said.

Fluctuations in blood pressure are a physiological response to any form of activities or stress. Physical stressors such as pain or discomfort and exercise, as well as anxiety, will cause the pressure to rise.

Prof Tan said: "When a patient with Covid-19 is hospitalised and experiencing cough or breathlessness, he or she will have fluctuating blood pressure. Maintaining stability in the pressure will be a challenge in patients with concurrent heart diseases or other underlying medical conditions (such as hypertension)."

Dr Mak Koon Hou, SHF assistant honorary secretary, cited studies of Covid-19 patients and said the findings suggest that "patients with hypertension were more likely to succumb to a more serious form of Covid-19".

However, Prof Tan said there is no reason to suggest that hypertension causes a person to be more susceptible to Covid-19 itself.

REASSURING CONCLUSION

Earlier studies in China suggest that a class of hypertension medicines known as angiotensin-converting enzyme inhibitors and angiotensin receptor blockers increased the susceptibility of patients to Covid-19.

These medicines are commonly used to control hypertension, improve heart function in those with heart failure and prevent progression of kidney failure.

Dr Mak said: "These studies suggest that patients with certain blood pressure-lowering medicines may increase an enzyme, which is needed for the Sars-CoV-2 (the strain of coronavirus that causes Covid-19) to enter the cells to cause the disease. The finding gave rise to the hypothesis that those receiving these medicines were more susceptible to Covid-19."

This led to the rapid widespread dissemination of the risks of those with Covid-19 and hypertension, said Dr Mak.

However, a study by researchers from the New York University Grossman School of Medicine in New York and collaborating institutions has drawn the reassuring conclusion that there is no association between the common blood pressure drugs included in the study and the risk of Covid-19.

The research was published in The New England Journal of Medicine last month.

Prof Tan said: "While there may be theoretical basis for such risks, this did not show up in at least four different well-corroborated research studies which have since been published."