The message is everywhere — take vitamin C.

It’s added to everything from candy to cold cures. Labels for bottled drinks boast, “Four lemons’ worth of vitamin C!” There’s even a fancy restaurant that features “vitamin C desserts.”

Meanwhile, sales of vitamin C supplements have skyrocketed.

But how much vitamin C should you be ingesting per day?

This is actually one of the most controversial questions about this essential nutrient.

This month, Japan is doubling its recommended dietary allowance (RDA) for vitamin C from 50 mg to 100 mg per day for adults. The United States is also expected to raise its RDA from its current 60 mg to more than 100 mg, possibly 200 mg.

Against the backdrop of this change lies an accumulation of research on the vitamin.

The old benchmark was set to prevent scurvy, a vitamin C-deficiency disease that killed thousands of people in Western countries through the 19th century. Previous studies had shown that ingesting 50-60 mg of vitamin C per day was enough to prevent the disease, whose symptoms include various mental and physical disorders, such as fatigue, depression, gum bleeding and slow wound healing.

“But vitamin C has been found to be involved in a much wider range of bodily functions,” says Saga University professor Akira Murata, a leading researcher.

To date, researchers have found proof that vitamin C helps the body manufacture collagen, metabolize a protein-building amino acid and form hormones that control stress levels, digestion and reproduction. It is also found to be a powerful antioxidant that protects cells against cancer-causing free radicals.

Despite these findings, there is still no conclusive evidence that shows the benefits of taking different amounts of vitamin C, experts say. “This is sought by many laboratories now around the world, including mine, but we have no direct information yet,” says Mark Levine, another leading researcher at the U.S. National Institutes of Health.

So the new recommendation is in fact based on various indirect evidence. One basic idea is to “take enough vitamin C so that the body is always saturated with it.”

A detailed study by Levine’s group with human subjects found that tissues were saturated with vitamin C when about 100 mg were ingested. Vitamin C levels in the blood also dramatically increased, as subjects raised their daily intake of vitamin C to 200 mg, after which the rate of increase slowed.

“A very small change in the amount ingested will make a large change in results [up to 200 mg],” Levine says. “The [old] recommendation is on the lower third of the curve.”

A daily intake of 100 mg is the most efficient dosage to saturate tissues, Levine said. He proposed an optimal daily intake of 200 mg so that not only tissues but blood approaches saturation.

There are some vitamin enthusiasts who pop high-doses of vitamin C pills — 500 mg, 1 gram, even 10 grams — every day. Ever since two-time Nobel Prize winner Linus Pauling published a book touting the medical benefits of the vitamin, megadoses of vitamin C have been promoted as a remedy for almost everything, from the common cold to cancer and heart disease.

Numerous clinical studies have been done, but experts largely agree that there is no solid scientific basis for taking megadoses of vitamin C as supplements.

“Are there direct benefits from vitamin C itself? For heart disease, cancer or cataracts? Data are not sufficient. Not yet,” Levine said.

Although the vitamin is known to be a remarkably safe material, some research has pointed out possible harm from overdosing on vitamin C supplements, such as diarrhea and kidney stones.

So what experts recommend is simple: Look to nature for your vitamins. Take as much vitamin C as possible from food to reach at least the RDA level.

Epidemiological studies of people consuming a plant-rich diet high in vitamin C have shown that they have a lower cancer and heart attack rate than those with a vitamin-poor diet. Fruits, vegetables, whole grains and nuts are also loaded with other vitamins and nutrients in addition to vitamin C.

“There are many, many experiments that associate fruit and vegetables with decreased cancer of the gastro-intestinal tract and maybe the respiratory tract,” Levine said.

It is important that vitamin C be consumed every day since it is not a fat soluble vitamin, and cannot be stored in the body for later use. Murata suggests that people try to ingest more vitamin C than the recommended amount since the vitamin in food is partially destroyed by cooking. “Large amounts of vitamin C are also consumed through smoking, stress and medication,” he said.

In line with COVID-19 guidelines, the government is strongly requesting that residents and visitors exercise caution if they choose to visit bars, restaurants, music venues and other public spaces.