Fauci though, does, advocate taking a couple of vitamins, especially with a pandemic still raging and given we all need to shore up our defences. “If you are deficient in vitamin D, that does have an impact on your susceptibility to infection. So I would not mind recommending it,” he says.

Aged 79, he takes vitamin D himself. A September 2020 study by the University of Chicago Medicine lends weight to his advice: it found a link between vitamin D deficiency and vulnerability to Covid-19.

Sally Poon, a Hong Kong-based dietitian, notes that dietary supplements, as their name suggests, “are intended to supplement the diet”. There are circumstances where one may benefit from taking them, she says, and cites as an example people with allergies or food intolerances. People with lactose intolerance may be calcium deficient, for instance.

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Vegans often lack vitamin B12 and may benefit from taking extra, and people who are diagnosed with a specific deficiency through a blood test may need to augment their diet. Those with anaemia need to take iron, for example, and folic acid is important for women planning to become pregnant, and during early pregnancy to prevent neural tube defects in the unborn.

These included babies who were exclusively breastfed – because consumption of human breast milk alone doesn’t meet requirements; people with darker skins; people with conditions that limit fat absorption (vitamin D being fat soluble) and those whose sun exposure may be limited because they are homebound, or wear long robes and head coverings for health reasons or because the weather is cold.

The supplements industry is largely unregulated, unlike the food and drug industries. So we should be careful about our choices, says Dr Paul Ng, a Hong Kong specialist in gastroenterology and hepatology.

“The keys are moderation, and to know what you’re missing and what you’re doing,” he says. As a general principle, he suggests taking a supplement to overcome a deficiency – but to confirm a deficiency with a blood test rather than relying on symptoms.

Why take anything if we are not vegan or anaemic or suffering with a lactose intolerance? Do we not get what we need from a healthy diet? Michelle Lau, registered dietitian and founder of nutrition consultancy Nutrilicious in Hong Kong, says: “I’m all about a fresh, natural, whole-foods-first approach, but at the end of the day we aren’t perfect and there are certain nutrients that are difficult to get adequately from diet alone.”

Lau notes: “We’re busy and don’t have time, always, to be mindful of our diets … we have kids who won’t eat their greens … sometimes we cook those greens ourselves for too long [because we are so busy and get distracted] and boil away the goodness.”

Like Poon and Fauci, Lau stresses the importance of getting enough vitamin D. We can get it from a few food sources – eggs, some dairy products, certain mushrooms, salmon – she says, but most Hongkongers don’t get enough vitamin D because they aren’t eating enough of these foods. She recommends a multivitamin, as an “insurance base”, and Omega-3 fatty acids to keep the brain and heart healthy.

“Evidence-based supplements are fine, but sometimes people are interested in supplements that may have less research supporting their use, or take supplements that their friends or family members are taking without considering their own needs,” Lau says.

“Over-supplementation can be dangerous. Some vitamins are water-soluble (such as vitamins C and B complex), and any that your body doesn’t need will leave your body through your urine. On the other hand, fat-soluble vitamins [A, D, E and K] are stored in the body for long periods of time and generally pose a greater risk for toxicity than water-soluble vitamins. For example, high amounts of vitamin A consumed during pregnancy can lead to birth defects.”

So how do you know how much to take if you’re going to take any? Cardiologist Dr David Jenkins, a British-born professor in the department of Nutritional Sciences at the University of Toronto in Canada, has explored the impact of vitamin and mineral intake on heart health.

In a 2018 study, he concludes that “the current data on supplement use reinforces advice to focus on healthy dietary patterns, with an increased proportion of plant foods in which many of these required vitamins and minerals can be found”.

Jenkins said that vitamin percentages are easy to get right, so vitamin content on reliable brands is mostly accurate – just be aware of what you need in what amounts.

Poon also warns that, aside from taking vitamins in the right amounts for your own personal needs, you must be mindful that seemingly benign vitamins and supplements can be dangerous if you’re taking prescription medication.

Vitamin K, for example, can interact with the blood thinner Warfarin – vitamin K promotes clotting while warfarin reduces it and is taken by people who bear a clotting risk such as stroke.

St John’s wort can speed the breakdown of many medicines and reduce their effectiveness – including some antidepressants, birth control pills, heart medications, anti-HIV medications, and transplant drugs.

Studies show that smokers who take high doses of beta-carotene supplements have an increased risk of lung cancer.

Vitamin E supplement does the opposite of vitamin K and can increase the risk of bleeding in people taking anticoagulant or antiplatelet medicines, such as warfarin.

Taking iron and/or calcium supplements with the drug levothyroxine, used to treat hypothyroidism and other types of thyroid disorders, can reduce this medication’s effectiveness. It should not be taken within four hours of having had iron and/or calcium supplements.

Ng suggests treating supplement pills as drugs, just like any other pills.

“Everyone should ask themselves – ‘why, what, how much, and for how long’ before starting a supplement. There is no one-size-fits-all here, and don’t simply follow the crowd into the next thing that’s trending.”