Goji berries may prevent age-related vision loss
Regular intake of goji berries will prevent or delay age-related vision loss1. One just has to eat about 28g (a handful) five times a week.
It seems like the goji berries are acting like sunscreen for your eyes to protect them from potential blue light damages.
Most people have heard of "blue light", though how damaging is it really to our health?
How bad is blue light?
Blue light, with relatively high energy, can cause irreversible photochemical damage to eye tissue. Excessive exposure of the eye to blue light tends to cause a series of alterations, such as oxidative stress, mitochondrial apoptosis, inflammatory apoptosis, mitochondrial apoptosis and DNA damage, resulting in the development of dry eye disease, glaucoma, and keratitis.2
This might sound concerning though the wording is important. First of all the blue light has to be "relatively high energy". Most devices with a screen or LEDs don't come anywhere close to the number needed.
However, the intensity of solely the 470 nm wave length of blue light from the LEDs is 0.14 W/m², only a fraction of the 470 nm of light emitted on an average sunny day (1.79 W/m²)3.
How concerning is blue light from the sun?
Since the energy of the blue light from the sun is more the 10x the energy from LEDs, this would conclude that we should stay away from sun light.
This is counterintuitive to the fact that sunlight is needed for us to synthesis vitamin D34. Here the factor is time exposure. Since too much exposure may cause skin cancer. Thus it could be hypothesized that the sunlight doesn't just damage our skin but also our eyes.
On the other side, sunlight is not purely blue light, but comes in a spectrum of light, 100 nm to 1 mm4. This spectrum includes the ultraviolet, visible range, and the infrared range.
How can one countract the negative effects of blue light?
It has been shown in situ or in vitro that red light counteracts the negative effects of blue light3.
This means one can either use red LEDs or even the sunlight for this fix.
red light from a computer screen or on a sunny day is respectively, 0.007 W/m² and 1.62 W/m²3.
This still results in 0.17 W/m² difference in favor for blue light for the sun. Thus one could use infrared lamps with high energy to counteract these potential negative effects.
Until now we have been focusing on the energy of the light. It was only briefly mentioned that time is a factor. Thus we will look at that next.
How long does one have to be exposed to blue light to experience negative effects?
Many have experience a sunburn fairly quick after being exposed to sun without protection, which is maninly due to ultraviolet rays, which are below the blue light (420–490 nm) spectrum3.
On the cell level in vitro studies have shown cell death when exposed long term to blue light5. The data suggest that
After long-term blue light exposure, the percentage of early apoptotic cells at 14 h was 29.2 %, at 22 h was 79.2 %, and at 24 h was 85.4 %5
which was done with 5 W/m².
Although blue light is a big part of our day-to-day lives, the math suggests that the exposure to blue light is not a big concern.
Let 0.13 - 0.3 W/m² be the energy of blue light we are exposed to on average per day. Assuming energy is accumalative per day, then it would take 16 - 38 days until the same strength of energy is met as in the last question.
Then on top of that, 24 hours of exposure is equivalent to an average of 1.5 days, assuming one sleeps 8 h per day. This increases the day count to 24 - 57 days.
The main cells that are exposed to potential damage is the epidermis, the top layer of skin. The epidermis completely replaces itself every 30 days6. Meaning in the worst case, there is a 20% chance that one is causing premature cell death.
Most of these studies were done in vitro on cell cultures. This means that they probably won't hold up in vivo.
Further in the previous "worst case" scenario, you are looking at 24 days of uninterrupted sunny days and being outside for at least 16 hours a day. It is very unlikely that anyone will fall into this category.
One could conclude that blue light has no concern in our day-to-day life, though age and other factors like smoking could tell a different story7. This would suggest that locations that deal with high air polution would fall into the same category as smoking.