The study involved more than 40,000 current and former male smokers. The current smokers who consumed five or more servings of fruits and vegetables every day were 40% less likely to develop the lung disease compared to smokers who only ate two servings or less.

Each additional serving of fruits and greens was tied to an 8% risk reduction.

Lead author Joanna Kaluza of the Karolinska Institute in Stockholm suggests that current and former smokers should eat as much fruits and vegetables as possible as each serving significantly decreases the risk of COPD development.

COPD is a category of lung diseases that make breathing difficult and can cause wheezing or coughing. The most common types of COPD are emphysema and chronic bronchitis, and they most often occur in smokers and former smokers.

The antioxidants found in produce might help to protect lungs from smoking damage, the researchers write in the journal Thorax.

The team studied data on 44,335 middle-aged and older Swedish men. None of the men included in the analysis had been diagnosed with COPD at the first assessment.

At the start of the study, the participants completed questionnaires detailing how often they ate different types of foods, including fruits and vegetables, as well as their smoking history. Researchers followed the men from 1998 to 2012 and used a patient registry to determine if they were diagnosed with COPD during the study period.

Almost two thirds of the men were current or former smokers and 1,918 were diagnosed with COPD by 2012.

The research team divided participants into five groups according to how many servings of fruit and vegetables they ate daily. The top fifth ate more than five servings per day, while the bottom fifth ate less than two servings daily.

After separating them again by smoking status, researchers found a significantly lowered risk of COPD tied to high fruit and vegetable consumption among smokers and former smokers, but not among never-smokers.

Ex-smokers with high consumption of greens were 34% less likely to develop COPD than ex-smokers with low fruit and vegetable consumption, and each additional serving was tied to a 4 percent drop in COPD risk.

When researchers analyzed the types of produce tied to lower COPD risk, they found an association with apples, pears, leafy greens and peppers but not with berries, citrus, tomatoes or onions.

We rely on antioxidants, such as those found in fruits and vegetables, to defend our lungs against harmful substances in cigarette smoke and air pollution, said Seif Shaheen, a professor of respiratory epidemiology at Queen Mary University in London who co-authored an editorial accompanying the study.

However, Shaheen stressed that diet is not a cure-all for the effects of smoking. “The most important thing you can do to reduce your chances of getting COPD is not to smoke/to stop smoking,” he said by email.

“Eating more fruit and vegetables is likely to be beneficial for your health in many ways, and for smokers who can’t stop smoking this may help to reduce your risk of getting COPD,” added Shaheen, who was not involved in the study.

“High fruit and vegetable consumption not only reduces the risk of chronic lung disease, but also cardiovascular disease, cancers, helps to keep proper body weight and other benefits,” Kaluza noted.

“It is possible for everyone to include more fruits and vegetables in their diet,” she said.

Researchers at the Karolinska Institute in Stockholm said that they had conducted a study showing how nitrate, found naturally in spinach and several other vegetables, tones up muscles.

For the study, which will be published in the Journal of Physiology, the research team had placed nitrate directly in the drinking water of a group of mice for one week and then dissected them and compared their muscle functions to that of a control group.

“The mice that had been on consistent nitrate had much stronger muscles,” they said in a statement.

The nitrate used “was equivalent to a human’s consumption of about 200 to 250 grammes of spinach a day, so it’s a very easily obtained amount,” one of the researchers at the Department of Physiology and Pharmacology, Andres Hernandez, told AFP.

“Well, it is if you eat spinach. For people who don’t eat their vegetables it will be more tricky,” he added.

While no effect could be seen in the so-called slow-twitch muscles used for moderate exercise and endurance, the scientists saw a clear change could be seen in the fast-twitch muscles used for strength and more high-intensity exercises, Hernandez said.

The tricky question, he said, was determining why this happened.

The researchers discovered that the nitrates had prompted an increase in two proteins, found naturally in the muscles, that are used for storing and releasing calcium, which is vital to making muscles contract.

The protein increase in turn led to higher quantities of calcium released in the muscles, Hernandez said, pointing out that “if you have more calcium released, you have a stronger contraction.”

Translated into human terms, consuming nitrates from for instance spinach increases the muscle strength available for things like lifting weights or sprinting up a steep hill.

It could also increase endurance, Hernandez said, pointing out that when stronger, the fast-twitch muscles, which fatigue faster than other muscles, do not need to contract as frequently.

This is not only good news for exercise buffs looking to improve their performance.

“The really exciting part is to go ahead and look at people with muscle weakness, with muscle diseases, and even aging, and see if this can actually improve their muscle function,” Hernandez said.

He said the research team aimed to conduct a few more studies on mice but hoped to also carry out studies on humans soon