Detecting deficiencies: New strategy could speed up mass testing of vitamin and mineral levels
Writing in The Journal of Nutrition, researchers analysed the levels of vitamins and minerals in 500 malnourished Nepalese children according to conventional methods, before using mass spectrometry methods to identify and quantify levels of proteins that are associated with vitamin deficiencies levels in the same samples.
The team were able to analyse many proteins in any sample at a single time, so cutting down the usually lengthy time it takes to test for nutritional deficiencies.
More than 30 vitamins and minerals are essential to human health, and conventional methods for measuring their levels rely on running multiple different tests for each person, explained Professor Keith West from Johns Hopkins University in the US - who led the study.
"Currently, levels of each vitamin or mineral are measured by different tests which are often performed in different labs, so the whole process can take three or four years to detect widespread deficiencies," said professor West. "That's too long to wait when the proper growth and cognitive development of children are on the line."
By focusing on the levels of proteins that specific nutrients interact with - rather than the nutrients themselves, West and his team are able to use fast and reliable mass spectrometry methods to speed up the process.
"Mass spectrometry allows us to measure the quantities of 500 to 1,000 proteins in the blood at one time," said Dr Robert Cole - co-author of the study.
"Not only that, we can mark all of the proteins from a single sample with a chemical tag that identifies them in the resulting data," he added. "Because there are eight different tags available, we could tag eight different samples and then mix them together and analyze the eight samples at the same time, directly comparing the samples and saving a lot of time."
Protein proxies
The time and cost involved in the current method to screen for nutritional deficiencies are high enough to be entirely prohibitive at the population level - especially in developing countries, said West.
To overcome this barrier his team focused on what all vitamins and minerals have in common: That each does its job by interacting with proteins throughout the body.
Because methods already exist for simultaneously identifying the levels of hundreds of proteins in a single sample of blood, the team wondered if some of those protein levels could be correlated with the levels of their associated nutrients, and thus act as 'proxies' for the nutrients.
Using blood samples taken from the 500 six to eight year old Nepalese children, the team first analysed the levels of vitamins and minerals according to conventional methods, and then used mass spectrometry to identify and quantify proteins levels in the same samples.
At the heart of their experiment lies the assumption that there are proteins in the bloodstream whose quantities reliably change with the levels of certain nutrients, said West.
For example, retinol binding protein (RBP) binds to vitamin A and carries it through the bloodstream to every part of the body, so the researchers theorised that levels of RBP in the children's blood would be a good proxy for their vitamin A levels.
To test this assumption, they compared their mass spectrometry results with those of conventional methods for measuring nutrient levels, and found that, for each nutrient, there were often not just one but several proteins whose levels were significantly correlated with the nutrient levels obtained by conventional means.
In the current study, the team focused on five nutrients (vitamins A, D and E, and copper and selenium) - however West suggested that there is reason to believe that other vitamins and minerals will also have good proxy proteins.
His goal now is to create a simple, portable test kit that would measure many proxy proteins from a single sample in a single test.
"That would allow us to determine the level of nutrient deficiencies in a whole population within a few months," West explained.
"Then we could implement a remedy, like fortifying foods with particular nutrients - something tailored to the needs and habits of the particular population - and then follow up with more tests later to make sure the remedy is working."
