Deep space missions, such as a manned mission to Mars, present significant radiation risks from exposure to high-energy cosmic rays and other ionizing radiation. Cary Zeitlin of the Southwest Research Institute and his colleagues have calculated that a 360-day return trip to Mars would involve a radiation exposure of 662 ± 108 millisieverts (mSv), equivalent to about 10,000 chest X-rays [1]. On Mars, radiation exposure is lower than in space but still higher than on Earth's surface. Mars has no global magnetic field comparable to Earth's geomagnetic field. Combined with a thin atmosphere, this permits a significant amount of ionizing radiation to reach the Martian surface.
Long-duration spaceflight also leads to bone loss, with physical exercise showing limited success in preventing it. Supplemental vitamin D may help maintain bone health during the 4-6 months of microgravity [2], and it could protect against various radiation damages [3] and could be potentially helpful in general cancer prevention [4] in such a 'radiation-soaked' environment.
This important compound of the human diet is primarily created in the skin during exposure to sunlight (to specific UV wavelengths) and can be found in a few dietary sources, mainly from animals (e.g. salmon, mackerel, tuna, egg yolk, beef liver). There is no way how to transport and use animal sources during the first missions and colonization attempts.
Astronauts can take vitamin D supplements to prevent its deficiency, but these supplements must be carried from the beginning, for the whole mission. Another option could be an artificial UV radiation source (to expose the skin to specific UV wavelengths), but a more effective and reusable method is using fungi exposed to UV rays [5].
When fresh mushrooms or dried powders are purposely exposed to artificial sunlight by use of an industrial ultraviolet lamp, vitamin D levels can be controlled - this process can lead to much higher levels of the vitamin created [6]. Researchers from Boston University School of Medicine (BUSM) have discovered that a normal serving (approx. 3 oz or 1/2 cup, or 60 grams) of fresh mushrooms treated with ultraviolet light has increased vitamin D content to levels up to 80 micrograms or 2700 IU if exposed to just 5 minutes of UV light after being harvested [7].
More detailed results [6]:
- Mushrooms, portobello, exposed to ultraviolet light, raw: Vitamin D2: 11.2 μg (446 IU)
- Mushrooms, portobello, exposed to ultraviolet light, grilled: Vitamin D2: 13.1 μg (524 IU)
- Mushrooms, shiitake, dried: Vitamin D2: 3.9 μg (154 IU)
- Mushrooms, shiitake, raw: Vitamin D2: 0.4 μg (18 IU)
- Mushrooms, portobello, raw: Vitamin D2: 0.3 μg (10 IU)
- Mushroom powder, any species, illuminated with sunlight or artificial ultraviolet light sources
(Shiitake fungi can be considered a superfood - food with supposed health benefits)
Growing mushrooms in space could provide an efficient way to incorporate vitamin D into astronauts' diets. The UV light source used could also serve other purposes, such as air purification and tool sterilization.
Mushrooms' growing process can be helpful in other ways like decomposing food waste and other organic materials. Mushroom cultivation requires relatively little light (thus it is less energy-consuming), making it energy-efficient and suitable for underground tunnels on Mars. Mushrooms could be part of a small, enclosed, food-producing biosphere on Mars.
UV emitting LEDs could be manufactured in Martian colonies using 3D printing processes, along with other LEDs with various wavelengths.
There are many processes aimed at artificially adjusting plant growth using different wavelengths. One notable example is exposing tomatoes to extra light from LED lamps, providing a supplementary dose of light similar to a quarter of the natural light intensity on a sunny day. This exposure has been found to increase the level of vitamin C in tomatoes [8]. Tomatoes are considered a cancer-fighting superfood.
Sources:
6. Vitamin D2