Masks, handwashing, and social distancing are key combatants, fending off attack from the outside. But healthy eating strengthens the warriors that keep us safe within.

It’s time to put nutrition on the frontline of the COVID-19 war, according to Manfred Eggersdorfer, PhD.

“I think we have to … follow social distancing, and also wear masks, but optimal nutrient status would be, in my view, an additional measure and help to reduce the risk for infections,” said Dr. Eggersdorfer, professor for Healthy Ageing at the University of Groningen, the Netherlands.

Dr. Eggersdorfer chatted with Medical Daily about his research on macronutrients and viral resistance, published in the journal Nutrients.

The paper looked at a wealth of information about how macronutrients influence immunity. The research goes well beyond the typical advice to max out on Vitamin C. The key players are not only C, but Vitamin D, zinc, and omega-3 fatty acids – all of which have been proven to strengthen the immune system.

The issue is under-appreciated on all fronts, said Dr. Eggersdorfer, who for many years directed research and development at DSM Nutritional Products.

“It is a pity that government authorities, nutrition societies, and scientists, do not take up this topic more. I am ... disappointed by the medical community because they should really also recommend to care for your diet, to care for optimum nutrition, and to care for optimal nutrient status as additional measures that reduce the risk for infections.”

But why?

“For immunity, we require a higher intake of some of the nutrients in order to have the best condition of the immune system,” he explained.

Vitamin C

Vitamin C revs up white blood cells, the killers that attack and dispose of invading microbes, Dr. Eggersdorfer said. “If they have a good reservoir of Vitamin C, they are more mobile and motile and better able to fight pathogens, viruses, and bacteria.” The usual recommended daily intake is 75-100 mg. But doses of 200 mg or more have been shown to reduce the risk, severity, and duration of respiratory tract infections. Already sick? Up it even more – 1 or 2 grams is the way to go.

Vitamin D

Our bodies naturally produce Vitamin D when we’re exposed to sunlight, but low levels are common, Dr. Eggersdorfer noted in his paper.

Vitamin D deficiency is associated with an increased risk of respiratory infections. Studies have confirmed the benefit of Vitamin D supplements. A review of 25 studies that included 11,000 subjects found that supplementation could cut the risk of infection by up to 70%.

Earlier this year, the New York Times reported a spike in sales of Vitamin D supplements.

One study recommended people at risk for COVID-19 rapidly raised their Vitamin D levels by taking 10,000 IU a day for a short period time. Broadly, the consensus seemed to be that:

  • Vitamin D deficiencies are common.

  • Vitamin D is linked with improved outcomes to respiratory infections.

  • Taking Vitamin D is safe and cost effective.

In September a group from Harvard Medical School launched a clinical trial. They hope to recruit 2,700 people to test if Vitamin D supplementation reduces the risk of hospitalization or death. People participating in the trial would take a large dose of Vitamin D for two days and smaller doses for the remainder of the four weeks.

The trial is slated to finish in 2021. Clinical trials are required to prove if a treatment is effective. While Vitamin D supplements may help, they are not a proven cure or a proven preventative measure.

Especially during the winter months, and during lock downorders, people are less likely to get high quality time in the sunlight. Here, supplements can make up for the loss. Guidelines typically suggest 600 IU/day, but Dr. Eggersdorfer suggests 2,000 IU/day would be a better bet.


Zinc lozenges may sound like an old wives’ tale, but they may be effective at reducing the duration of symptoms of a common cold. They work by reducing the amount of viruses in the nose and throat at the onset of a cold. A 2017 review of seven studies compared them with an inactive lozenge. The zinc lozenges reduced the length of the cold by 33%. The most effective dose was about 100 mg; higher doses didn’t work any better.

But just this year, a study comparing active to inactive lozenges found that lozenges don’t shorten the duration of colds. Placebo-controlled studies like this are considered the gold standard for determining if a treatment is effective. So the jury is still out on lozenges. However, since zinc supplements increase the formation and lifespan of immune cells, there may be an overall benefit. Children in particular are more resistant to respiratory infections and some diarrheal infections when zinc levels are up to par, Dr. Eggersdorfer said.

He recommends 8–11 mg/day.

Fatty fish are your friend

In addition to vitamins, Dr. Eggersdorfer believes people should add in omega-3s, “you can get this normally from fish oil or eating fish, but we recommend 250 milligrams,” he said.

The plate

But, is supplementation the only way to reach these goals? The short answer is no. For some things, like Vitamin C, getting the full 200 mg is incredibly easy, “200 mg you can achieve if you eat every day, maybe two oranges or an orange and a kiwi fruit,” Eggersdorfer said, “to achieve an intake of 200 milligrams of vitamin C is possible via diet.” According to a USDA report, the body doesn’t seem to absorb much more than 200mg of Vitamin C a day, and over 3 grams (3,000mg) might even be unhealthy. There are about a hundred milligrams of Vitamin C in a large orange, so as long as people avoid eating thirty oranges in one day, Vitamin C is easy to get from food and hard to overdo.

Vitamin D is a different issue. It is not as easy to get from food, especially in the winter, to get from the sun. For many, the supplement aisle might be the most convenient place to look. Eggersdorfer explained that as for zinc and omega-3s, it would be possible to get them from meat and fatty fish. This takes commitment, one fatty fish meal a week is unlikely to be enough fish to supply adequate omega-3s.

Going it alone

In the same way scientists know how much of a vitamin or mineral is too little for the human body, they also know what is too much. These are called upper limits, and so while some of a certain vitamin, like 2000mg of Vitamin D, is good, too much, 4,000mg for Vitamin D can do damage. Nutrition is a delicate tightrope and people who are interested in supplementing should check with their doctors. Not only can a doctor test someone’s levels of vitamins and minerals, they know about possible interactions with medication and optimal levels for each patient.

At the grocery store

As for picking a supplement, go for one that doesn’t promise extraordinary health claims, and look for a trusted brand.

Eating To boost health

What does a health expert eat? Muesli apparently. Dr. Eggersdorfer said he starts the day with supplements and a mix of oats and grains. After that, it’s lots of vegetables and a light dinner.

The take home

Especially for people getting outside less, or eating fewer fruits and vegetables during the winter, talking to a doctor about supplements might offer better health in the months to come. Getting better nutrition might protect the body and help the immune system, but wearing a mask and social distancing are proven ways to avoid getting or transmitting the coronavirus.

Sabrina Emms is a science journalist. She got her start as an intern at a health and science podcast out of Philadelphia public radio. Before that she worked as a researcher, looking at the way bones are formed. When out of the lab and away from her computer, she's moonlighted as a pig vet's assistant and a bagel baker.

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