This blog is a place where I will translate interesting findings in biomedical and basic science research from scientific jargon to plain old English. The bottom line: You don't need a PhD to understand science!

Thursday, August 6, 2009

Pass the Orange Juice and Pass the Test

After spending five minutes in a typical grocery store, it is clear that food manufacturers and consumers understand the importance of proper nutrition: Neon blue drinks glow with 100% vitamin C; boxes of chocolate flavored cereal are pumped with iron and folic acid; even yoghurt has fiber added to the extra calcium and vitamin D.

With the mass-marketing of fortified sugar water and the diligent offering of Flintstone chewables, it comes as a bit of a surprise, at least to me, that a significant population of children might be vitamin C deficient. While recorded reports of scurvy in the western world are far and few between, recent studies indicate that vitamin C deficiency might not be as rare as we would like to think. Approximately one-third of young children are measured to have vitamin C deficiency in some populations.

Most people can probably guess that malnutrition can have detrimental effects on growth and development of the world’s youth. Although, how vitamin deficiencies specifically affect brain development and function is not so obvious. Indeed, malnutrition during fetal growth can result in cognitive disabilities of the child. Impaired development of the hippocampus, a brain center responsible for long-term memory, has also been observed.

Last week, Pernille Tveden-Nyborg from the University of Copenhagen reported a critical link between postnatal vitamin C deficiency and memory retention in guinea pigs, an animal model that, like humans, is unable to generate its own vitamin C.

While people envision vitamin C as a glass of orange juice or a small round pill, to the cell, vitamin C is the superhero antioxidant that fends off DNA damaging free radicals. Cells risk severe damage, if not complete obliteration, without a counterbalance to the oxidative injury that occurs to proteins, lipids, and DNA in the presence of dangerously paired oxygen molecules floating around the cell.

Based on a previous finding that the brain of neonatal guinea pigs is particularly vulnerable to oxidative stress during vitamin C deficiency, Tveden-Nyborg hypothesized that sufficient levels of vitamin C are critical for normal brain development. To test this hypothesis, Tveden-Nyborg and colleagues raised guinea pigs that experienced chronic vitamin C deficiency during early postnatal life. Subsequently, two month old vitamin C deficient guinea pigs were compared to nourished controls in the Morris Water Maze, a task designed to test memory and spatial navigation.

The Morris Water Maze consists of a dark pool measuring 1.5 meters in diameter. If four quadrants are imagined in the pool, a small platform is placed at the center of a single quadrant 12 cm below the water’s surface. On day one, each guinea pig is randomly placed in the pool and trained to find the platform, which both nourished and vitamin C deficient guinea pigs do equally well. After four days of no training, the guinea pigs are retested for their ability to remember the location of the platform in the pool. Only this time, the platform is sneakily removed! Measurements are recorded on the length of time it takes each guinea pig to enter the proper quadrant, how long each guinea pig remains in the quadrant, the number of times the guinea pig crosses the previous location of the platform, and the average distance the guinea pig swims from the target site, presumably trying to find the missing island.

Tveden-Nyborg found that the guinea pigs with proper vitamin C supplementation performed significantly better than guinea pigs exhibiting vitamin C deficiency on all measurements, suggesting that early postnatal vitamin C deficiency impaired the guinea pig’s spatial memory later in life.

Both spatial navigation and long-term memory are controlled, in part, by the hippocampus, a distinct compartment found on the side of each brain hemisphere. When Tveden-Nyborg and colleagues studied post-mortem hippocampus preparations, they found a significant decrease in the number of neurons present in sections of the vitamin C deficient brains as compared to the controls. At this time, it is unclear if the decreased neuron number is due to an increase in cell death, a lack of normal cell division, or both.

While the results from these experiments in Guinea Pigs do not directly provide information about human development, they certainly indicate that nutritional requirements for early brain growth and function is an area that warrants further investigation.

So, for those picky-eaters who won’t touch anything that can be grown in the backyard, perhaps some Juicy Juice and a Flintstone vitamin isn’t such a bad idea after all.

Tveden-Nyborg et al. “Vitamin C deficiency in early postnatal life impairs spatial memory and reduces the number of hippocampal neurons in guinea pigs.” Am J Clin Nutr. doi: 10.3945/ajcn.2009.27954.

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