Aging is a process that is as universal as a process can
be. Everything ages, all animals,
plants, even planets and the universe as an entity age. It is something we cannot avoid,
despite the many searches for a fountain of youth. And as we age, we may or may not become afflicted with the
many complications that accompany getting old. Our joints start to get stiffer, our muscles get a little
weaker, and our memories might get a little worse. However, these conditions aren’t all or none, and there are
many things we can do during our lives to help decrease the amount of function
we lose in old age. These include
eating a healthy diet, exercising regularly, and managing stress.
One complication of aging I’d like to discuss today is our
eyesight. This one thing I am sure
most people would like hang on to for as long as possible, since, as humans, we
rely on our eyesight more than any of our other senses. We have all seen eyesight that
deteriorates in old age, many people start to need glasses when they never did
before, or it might be getting harder and harder to see street signs while we
are out driving.
This type of loss of sight is known as age-related macular
degeneration (AMD), and is a phenomenon that plagues millions of people every
year. However, the exact causes
and the development of this disease aren’t clearly known, so finding treatments
and prevention plans for it is very difficult. But, like many diseases of civilization, this one has inflammation
as a root cause.
How
AMD is an inflammatory condition
There are many intersecting lines of evidence that help to
show the inflammatory nature of AMD.
The first we will discuss is parainflammtion caused by ROS production.
Since certain parts of our retinas are comprised of a large amount of neural
cell types along with photoreceptors the energy needs of this tissue is very
high (1). This will create a high metabolism in
these tissues, which can easily start to create ROS when energy is in constant
excess. As we have seen before,
these ROS can then damage the retinal tissues, and cause inflammation. Additionally, these ROS can be developed
by a process called photooxidation, which the energy from the light itself
excites the oxygen species, turning them into ROS. The presence of ROS causes
new blood vessel growth to occur, and this can result in choroidal
neovascularization (CNV), which is another form of AMD.
Next, certain components of our immune systems “complement
system” have been implicated in AMD.
By far the most well known complement is CRP, or C-Reactive protein,
which is a common biomarker for inflammation. Another complement implicated in AMD is complement factor H
(CFH). An interaction between a
certain genetic variant of CFH and CRP has been shown to be a main cause of AMD
in over 50% of cases (1). However, this interaction has been
shown to be most dangerous at CRP levels >3mg/L.
There are several other additional lines of evidence that
support the hypothesis that AMD is inflammatory in nature. Most of these are based on
anti-inflammatory treatments improving AMD in patients, or other diseases known
to be inflammatory in nature increasing the risk of AMD.
One twin study found that smoking, which is known to
drastically increase inflammation and the risk for a host of diseases, was
highly correlated with AMD. In
fact, the risk factor was 32% greater in smokers than in non-smokers (2).
The same study also looked at the effects of omega-3
consumption on AMD risk. The
omega-3 DHA is found in high concentrations in many of the photoreceptor layers
of the human retina. It is also an
anti-inflammatory, which can help to reduce AMD risk. In the twin study, they found a preventive effect of 22% by
those who consumed the most omega-3s compared to those who consumed the
least. This effect was even amplified
by those who consumed low omega-6s in their diet as well (2).
Since ROS production is on of the primary drivers of the
inflammation implicated in AMD, supplementation with various anti-oxidants has
been shown to help AMD (3). Other lifestyle modifications such as
quitting smoking, and losing weight if overweight or obese have been shown to
lower the risk for AMD.
The
effect of light on AMD
As many of us know, the light that comprises the visible
spectrum in composed of many different wavelengths, with each color being its
own distinct wavelength. Additionally, the visible spectrum leads into the infrared
spectrum at its low energy end, and into the violets and ultraviolets at its high-energy
end. However, not all wavelengths
of light are created equal to our photoreceptors. It turns out that the blues, violets, and ultraviolets are
actually damaging to our photoreceptors (4). In fact, our eyes have developed a way
to deal with this as we age, and that is to turn our lens slightly yellow in
order to block out some of the blue light. This study modeled the effects of adding certain filters to
a model of the retina, and measuring the ROS production, beginning at age
70. As we can see on the far right
of the graph, when no filter is used we have fairly high rate of ROS
production. However, when a yellow
filter is added to block out blue light, we get a decrease in ROS
production. An even greater
reduction in ROS production is seen when we filter out UV light, as seen by the
white diamonds that are virtually on the x-axis in the bottom right corner.
Another interesting experiment into the effects of light
used photobiomodulation, or providing specific wavelengths of light to elicit
certain signaling effects, on mice (5). In this they exposed
mice to a “damaging light”, which, interestingly, was just a regular 18W
fluorescent light. They then treated this light damage with three different
near-IR light treatments, one that was only done before the damaging light, one
during, and one after. They then
looked at the number of immune cells in various parts of the eye, and you can
see what an effect the damaging light (the LD treatment) had on the mice.
I think with these studies on the effects of light on our
eyes we can see just how important it is to limit our blue light exposure. This is a very common type of light
emitted from our computer screens, phones, TVs, and almost all other
electronics. You can pick up some
nifty yellow tinted glasses to help block out the light, and as geeky as they
might seem now, being able to see when you’re 70 or 80 is probably worth
it! Otherwise, just trying to
limit the amount of time we are exposed to these sources that emit mainly this
type of light is something we should all try to do. You can also download F.lux for your computer screen, but I
haven’t yet found a good app for my phone for it (I have an android, it looks
like you can jailbreak iPhones to get it on there).
Another important thing to note is just how important
crubing inflammation and supporting our immune systems are to all facets of
health. By doing this and keeping
our energy levels in check we can help ourselves age more gracefully, and avoid
many of the complications of our current industrialized way of life.
