Carrots are a great source of vitamin A which is derived effectively from the rich source beta-carotene contained in them. However, a new study has now revealed that to get full benefits of this so-called super-food, there is a need for an active enzyme to yield this vitamin.
Beta-carotene is a bioactive compound that provides carrots their orange colour. Previous studies in mice and humans have found that the conversion of beta-carotene to vitamin A lowers bad cholesterol in the blood. It is, therefore, believed that beta-carotene is able to protect us from atherosclerosis development which results from fat and cholesterol accumulation in our arteries.
Professor Jaume Amengual, assistant professor of personalised nutrition at the department of food science in human nutrition at the University of Illinois, has mentioned in the study that atherosclerosis is one of the main causes of death around the world.
Prof Amengual and his colleagues conducted two studies to further understand the effects of beta-carotene on heart health. The research team essentially confirmed that they detected a critical step along the process of beta-carotene being converted to vitamin A, for absorption in our body. The study reports that beta-carotene converts to vitamin A with the help of beta-carotene oxygenase-1 or BCO1, a type of enzyme.
Prof Amengual explains that a genetic variation within a particular person indicates whether one has a comparatively active version of BCO1. It has been hypothesised by the research team that those who have lesser quantities of the active enzyme would, perhaps, need other vitamin A sources in their diet to maintain a proper balance.
One of the two studies which the Journal of Nutrition has published, examined blood and DNA samples from more than 760 healthy young adults, whose age ranged from 18 to 26 years. Their initial analysis of the data confirmed a link between BCO1 activity and bad cholesterol level. Prof Amengual further confirmed that those who had a genetic variant linked to making the enzyme BCO1 more active were found to have lower cholesterol in their blood.
To put their findings to further test, the research team conducted another study, published in the Journal of Lipid Research, this time, using mice as the subject of the study. Since, in the human study, they observed that cholesterol was, indeed, higher in those who did not process much of vitamin A, it was essential to do a follow-up study to observe the impact over a longer period of time and genuinely assess whether these people developed any cardiovascular diseases later on. The team realised that it was not possible to do in a real-life situation and hence, considered mice as the ideal subject to fast-track the process.
"The main findings of the mice study reproduce what we found in humans. We saw that when we give beta-carotene to mice, they have lower cholesterol levels. These mice develop smaller atherosclerosis lesions, or plaques, in their arteries. This means that mice fed beta-carotene are more protected against atherosclerosis than those fed a diet without this bioactive compound," Prof Amengual explained.
In the second study, the researchers also investigated the biochemical pathways of these processes, determining where the effect occurs in the body.
"We narrow it down to the liver as the organ in charge of producing and secreting lipoproteins to the bloodstream, including those lipoproteins known as bad cholesterol. We observed that in mice with high levels of vitamin A, the secretion of lipids into the bloodstream slows down," Prof Amengual said.
Understanding the way the BCO1 enzyme relates to cholesterol has important implications. Normally, high levels of beta-carotene in the blood are linked to numerous health benefits. However, it could also be an indication of a less active BCO1 enzyme that is not converting the beta-carotene we consume into vitamin A.
In the research, Prof Amengual has noted that up to half of the population has a less-active variant of the enzyme. This leads us to believe that such people would be slower in processing vitamin A from a plant source and they would have to get this nutrient directly from an animal source, like cheese or milk, among others.