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Folic acid, B12 & Vision in Astronauts | Omega-3s & Brain Volume

Visual Changes Post-Space Flight May be Due to Altered Folic Acid & B12 Metabolism

About 20% of astronauts who’ve been on International Space Station (ISS) missions have developed ophthalmic changes after flight, including optic disc edema, globe flattening, choroidal folds, hyperopic shifts, and cotton wool spots. But why are some but not other astronauts affected? NASA researchers in collaboration with several universities have conducted experiments on ISS since 2006 to answer this question.

The investigative team found biochemical differences in crewmembers with vision issues, which strongly suggest that their folate and vitamin B12 dependent 1-carbon transfer metabolism was affected before, during, and after flight. One-carbon metabolites, including homocysteine, were 25-45% higher (P, 0.001) in those with ophthalmic changes than in those without them, and crewmembers with vision issues had consistently lower serum folate during flight. Pre-flight levels of homocysteine and cystathionine, and in-flight levels of folate, correlated with changes in refraction observed after flight (1).

The researchers believe that common polymorphisms in enzymes of this pathway (e.g. MTHFR 677C/T) interact with the shift in cranial fluids encountered at “zero” gravity in space to cause these ophthalmic changes.

While it’s not likely that you’ll encounter an astronaut in your waiting room anytime soon, these findings may have clinical import to those on Earth as well.

One of the most studied polymorphisms in this pathway is MTHFR 677C/T, which has an allele frequency of 30% in many ethnic groups. Heterozygotes (C/T) have a 30% decrease in the activity of the enzyme MTHFR and homozygotes (T/T) a 60% decrease in this critical enzyme. Evidence suggests that individuals with these polymorphisms may require more folic acid to maintain their status of this B-vitamin.

While Americans are getting more dietary folic acid than ever due to food fortification, getting some extra folic acid via a multi-vitamin supplement may be a good idea considering the high frequency of the polymorphisms, and that elevated homocysteine is a risk factor for ischemic stroke, inter-cranial aneurysms, migraine headaches, and possibly occlusive retinal vascular disease and some types of glaucoma. Many could also benefit from supplemental B12 due to the difficultly of its absorption in older people.

Brain Volume Tied to Omega-3 Intake

According to new findings, low blood concentrations of the omega-3s are associated with smaller brain volume and poorer performance on mental acuity tests (2).

Researchers from UCLA looked at the fatty acid content of red blood cells from over 1,500 men and women who were free of dementia and averaged 67 years of age. MRI scans were used to measure brain volume and white matter hyperintensities, a radiological finding that indicates vascular damage.

Study participants in the lowest quartile of omega-3 blood levels were observed to have significantly smaller total cerebral brain volume compared to those in the top quartile – a finding that held even after adjusting for age, smoking, body mass index and other variables.

Those with low omega-3 also fared poorer on tests of visual memory, abstract memory and executive function, defined as the control and management of other cognitive processes.

The investigators believe that the omega-3’s reduce vascular pathology and thus slow down the rate of brain aging. Too little omega-3 could promote accelerated brain aging.

Few people in the study used fish oil supplements, so the benefits were due to consuming more oily, cold-water fish. It may be that omega-3 supplementation could benefit brainpower – as well as cardiovascular health and perhaps vision maintenance – for those getting insufficient omega-3s from diet alone.

References

1. Zwart SR, et al. Vision changes after spaceflight are related to alterations in folate and vitamin B-12 dependent one-carbon metabolism. J Nutr 142: 427–31, 2012.
2. Tan ZS, et al. Red blood cell omega-3 fatty acid levels and markers of accelerated brain aging. Neurology 78:658-64, 2012.