What's more, the study found, both beta-carotene and vitamin E might offer some lung protection to heavy smokers.

Beta-carotene is an antioxidant compound that gives foods such as carrots, sweet potatoes and cantaloupe their orange and yellow coloring; the nutrient is also found in some greens, like spinach and broccoli.

The new findings suggest that non-smokers and smokers alike should get plenty of fruits and vegetables in their diets, according to lead study author Dr Armelle Guenegou of the French national health institute INSERM, in Paris.

Lung function naturally starts a slow decline around the late 20s, but a healthful diet may help the lungs stay more youthful, Guenegou told.

That does not mean, however, that smokers can avoid the consequences of the habit by eating well or popping vitamins. It is always best to quit smoking, Guenegou said, given the risks of lung cancer and cardiovascular disease.

A recent analysis of eight studies, for instance, concluded that beta-carotene, vitamins A, C and E, and other nutrients do not cut smokers' risk of lung cancer.

The new study, published in the medical journal Thorax, included 1,194 adults ages 20 to 44. At the outset, participants had their lung function measured, as well as their blood levels of vitamins A and E, beta-carotene and a related compound called alpha-carotene.

Lung function was gauged with an FEV1 score the amount of air a person can forcefully exhale in one second.

Overall, the researchers found, men and women with higher blood levels of beta-carotene at the study's start showed a smaller dip FEV1 scores over the next 8 years.

And among heavy smokers those who lit up at least 20 times a day higher levels of both beta-carotene and vitamin E were related to a slower decline in lung function.

Smoking generates excess levels of potentially cell-damaging substances called oxygen free radicals molecules that antioxidants like vitamin E and beta-carotene are designed to neutralise.

The body converts some of the beta-carotene is receives into vitamin A, while some is stored in tissues, including lung tissue. It's possible, Guenegou's team says, that beta-carotene in the lungs helps defend against the free-radical attack.

As for why vitamin E appeared protective only in heavy smokers, the researchers speculate that the vitamin jumps into a more potent antioxidant mode only when stress from free radicals is high.

Beta-carotene may also preserve non-smokers' lung function by battling free radicals, according to Guenegou. The potentially damaging molecules are a normal byproduct of metabolism, and they are also generated by outside sources other than cigarettes air pollution, for example.

The researcher stressed, though, that beta-carotene is not the sole player in lung or overall health. So it is important to get a mix of antioxidants and other nutrients from plant foods, rather than relying on pills.

Source: Thorax