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NUTRITION  AND  FITNESS

Humans, Fruit Bats, and Vitamin C

Blog Post #2, September 28, 2019

Photo: The straw-colored fruit bat Eidolon helvum just hanging out.

Fruit bats are beautiful, fascinating mammals. Also known as flying foxes, they are distinguishable from other bats by their dog-like faces. The largest fruit bats reach weights up to 3.2 lbs (~1.5 kg), and can have wingspans as large as 5.6 ft (1.7 m). Though they're mostly nocturnal, they use sight to locate food, instead of using echolocation. As their name indicates, their primary food source is fruit, although some species eat nectar, and some eat pollen and vegetation. Their hearts are capable of pumping at rates up to 700 beats per minute, without even drinking coffee! So, what do humans and fruit bats have in common? 

Humans and other higher primates, fruit bats, and guinea pigs are the only mammals that aren't capable of making their own vitamin C. All other mammals produce an enzyme in their livers that allows them to synthesize vitamin C from glucose (glucose is a simple sugar, the main product of photosynthesis, and is the most important source of energy for all life). We've lost the gene required to make this enzyme, apparently by consuming enough dietary vitamin C to avoid the need for it. This doesn't tell the full story however, since the small group of mammals that don't synthesize vitamin C help compensate using a special system for efficiently transporting it throughout the body. 

 A protein called Glut1 is uniquely found embedded in the cell membranes of our small 'group' of mammals' red blood cells. This protein allows blood cells to absorb vitamin C and transport it via the blood stream. Glut1 is not found in the red blood cells of mammals that can synthesize vitamin C, such as dogs, cats and mice. This protein greatly decreases the amount of vitamin C we must consume. Humans only need about 1 mg of vitamin C per kilogram of body weight per day, whereas goats for example, synthesize about 200 mg/kg/day.

Roles of Vitamin C

Vitamin C is essential for collagen production. Collagen provides structure and elasticity in our blood vessels, skin, bones, cartilage, tendons, and ligaments, and is the most abundant protein in the body. It is essential as an antioxidant for the neutralization of free radicals. Vitamin C 

Photo: The marianna fruit bat Pteropus mariannus shows off its contrasting colors

also assists in iron absorption; it acts as a chelate for iron in the stomach. Chelate is greek for 'crab's claw', and refers to the action of molecules that grab onto other molecules and increase their bioavailability. As chelated iron passes from the stomach to more alkaline areas of the digestive tract, it remains soluble. Another role of vitamin C is in supporting immune system function, due to its antioxidant capability and its complex role in cellular function. 

Dietary Sources of Vitamin C

Some excellent dietary sources of vitamin C include:

  • citrus fruits

  • kiwi

  • pineapple

  • Capsicum peppers 

  • white potatoes and sweet potatoes

  • leafy greens such as arugula

  • broccoli and other Brassica plants

Sources: