As with life itself, Vitamin E may be described in simple religious terms with a good and bad version alternately bringing health and harm.

In a new large study, Investigators at Northwestern University suggest the type found in canola, corn, and soybean oils is linked to a rising incidence of lung disease in the United States, whereas that found in sunflower and olive oils may do the opposite.

"Considering the rate of affected people we found in this study, there could be 4.5 million individuals in the U.S. with reduced lung function as a result of their high gamma-tocopherol consumption," study leader Joan Cook-Mills said in a press statement.

The allergy and immunology specialist also described the benefits of alpha-tocopherol, the good version of Vitamin E, in a paper published this month in the journal Respiratory Health.

"People in countries that consume olive and sunflower oil have the lowest rate of asthma and those that consume soybean, corn and canola oil have the highest rate of asthma," Cook-Mills said. "When people consume alpha-tocopherol, which is rich in olive oil and sunflower oil, their lung function is better."

Some 40 years ago, most Americans began substituting butter and lard in the kitchen for canola, corn, and soybean oils, as they were once thought healthier for the heart. As a result, average levels of gamma-tocopherol in blood plasma samples taken from Americans rose to four or more times higher than counterparts in European countries. Attendant with that rise, asthma rates had risen in the U.S. by 2010 to 8.4 percent, says the Centers for Disease Control and Prevention.

“The blood plasma showed how much they had acquired in their tissues," Cook-Mills said. "You get vitamin E from your diet or supplements."

In the study, Cooks-Mills and her colleagues analyzed data from more than 4,500 participants in the Coronary Artery Risk Development in Young Adults Study. She compared lung functioning tests taken at four intervals over a 20-year period to levels of gamma-tocopherol measured in blood plasma at three intervals over a period of 15 years. Similar to results seen in an animal model, higher levels of gamma-tocopherol were linked to a 10 to 17 percent decrease in lung functioning.

"A 10 percent reduction in lung function is like an asthmatic condition," Cook-Mills said. "People have more trouble breathing. They take in less air, and it's harder to expel. Their lungs have reduced capacity."

Yet the dichotomy between good and bad Vitamin E may now be explained by empirical observation, without recourse to mythology. A couple of years ago, Cooks-Mills identified the protein kinase C-alpha as the mechanism causing the health schism between the two types. As the protein binds to both types of Vitamin E, alpha-tocopherol inhibits its action while gamma-tocopherol once again goes the other way.

Source: Cooks-Mills, Joan M., Marchese, Michelle E., Kumar, Rajesh. The vitamin E isoforms α-tocopherol and γ-tocopherol have opposite associations with spirometric parameters: the CARDIA study. Respiratory Research. 2014.