WARNING!
This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.
I’ve written many articles detailing the general health benefits (and potential but largely avoidable risks) of sun exposure. But did you know sun exposure impacts your eye health as well? Here too, there are both risks and benefits, which largely prevents any hard and fast recommendations from being made.
Ultraviolet Light May Raise Your Risk of Cataracts
Starting with the risks, research1 funded by the U.S. National Eye Institute published in 2014 found ultraviolet (UV) radiation from the sun can damage proteins in your eyes, over time raising your risk for cataracts.
Cataracts develop when proteins in the lens of your eye unravel and get tangled together. Pigments also start to accumulate, clouding the lens and obscuring vision.2 As explained in the study’s abstract, UV radiation can trigger oxidation of proteins leading to cataracts:3
“Advanced glycation end products (AGEs) contribute to lens protein pigmentation and cross-linking during aging and cataract formation. In vitro experiments have shown that ascorbate (ASC) oxidation products can form AGEs in proteins. However, the mechanisms of ASC oxidation and AGE formation in the human lens are poorly understood.
Kynurenines are tryptophan oxidation products … present in the human lens. This study investigated the ability of UVA light-excited kynurenines to photooxidize ASC and to form AGEs in lens proteins.
UVA light-excited kynurenines in both free and protein-bound forms rapidly oxidized ASC, and such oxidation occurred even in the absence of oxygen … When exposed to UVA light (… 45 min to 2 h), young human lenses (20-36 years), which contain high levels of free kynurenines, lost a significant portion of their ASC content and accumulated AGEs …
Our data suggest that kynurenine-mediated ASC oxidation followed by AGE formation may be an important mechanism for lens aging and the development of senile cataracts in humans.”
UV Damage Implicated in Macular Degeneration
UV light damage has also been implicated in the development of age-related macular degeneration4 (AMD), the No. 1 cause of legal blindness in the elderly.
The Alienor Study,5 published in 2014, assessed how unprotected exposure to UV light over a lifetime might affect your risk for cataracts and AMD, concluding that people with the highest exposure levels over the previous 65 years had a 53% increased risk for cataracts and 59% higher odds for AMD compared to those with intermediate exposure. Dr. Rebecca Taylor, ophthalmologist and clinical spokesperson for the American Academy of Ophthalmology told Time magazine:6
“When you don’t wear protection, ultraviolet radiation you cannot see is penetrating the eye, and the eye structures are very sensitive to it. If you put a target in the center of the retina right behind the pupil, the macula would be the bull’s-eye. And when light comes into the eye, it hits that macula like a laser beam.”
Low UV Exposure Also Raises Risk of AMD
Importantly, however, subjects with the lowest exposure levels had an even greater risk for AMD — 69% — compared to those in the intermediate exposure group. This and other findings suggest the impact of sunlight on eye health is not all cut and dry. As noted by the authors:7
“This study further confirms the increased risk for cataract extraction in subjects exposed to high ambient UVR. Moreover, it suggests that risk for early AMD is increased in subjects exposed to high UVR, but also to low UVR, by comparison with medium exposures.”
The authors also cite two other studies that found the risk for AMD was actually lowest in subjects with the highest levels of UV exposure. In one,8 the inability to tan and sensitivity to glare were found to be “markers of increased AMD risk,” as these individuals were more prone to AMD and had lower levels of UV exposure overall compared to those without AMD.
Similarly, the second study9 concluded it could find no support for the claim that sun exposure increases the risk for AMD. Late AMD onset in particular was not associated with any particular light variable, while people “exposed to high ambient solar radiation and those with frequent leisure exposure to sunlight” had a 27% reduced risk of early signs of AMD.
The routine use of sunglasses did however decrease incidence of soft drusen — soft fatty deposits under the retina thought to be a risk factor for AMD.10 Other studies11,12 discussed in “Vitamin D3 Found to Rejuvenate Aging Eyes” suggest that optimizing your vitamin D status lowers the risk and helps prevent AMD by:13
- Inhibiting the accumulation of amyloid beta in your eyes
- Reducing retinal inflammation
- Reducing retinal macrophage numbers and altering their morphology (macrophages are immune cells that can cause inflammatory damage)
Early Sun Exposure Protects Against Nearsightedness
Studies have also found that spending more time outside early in life can help ward off myopia, better known as nearsightedness. According to a study14 published in JAMA Ophthalmology in January 2017, a mean increase in UVB exposure:
“… at age 14 to 19 years … and 20 to 39 years … was associated with a reduced adjusted OR [odds ratio] of myopia … No independent associations between myopia and serum vitamin D3 concentrations nor variants in genes associated with vitamin D metabolism were found …”
The researchers wrote that myopia is becoming increasingly common and is associated with complications that could ultimately threaten peoples’ eyesight. They added that while exposing oneself to sunlight is actually protective, most people are unaware of this fact.
To Wear Sunglasses or Not
When there are both risks and benefits, what do you do? I approach the issue of sunglasses the same way I approach vitamin D optimization. There’s overwhelming evidence to suggest unprotected sun exposure is important for optimal health, including healthy vision, but just like you don’t want to get a sunburn, you’d want to avoid intense UV radiation hitting your eyes for extended periods of time.
A sensible approach to vitamin D optimization is to expose a large portion of your bare skin until you turn the lightest shade of pink. After that, you cover up to prevent sunburn. This allows you to benefit from vitamin D production without risking skin damage.
Similarly, while routinely wearing sunglasses may do more harm than good, as the near-infrared wavelengths found in sunlight actually nourish and benefit your eyes,15 there are instances when sunglasses are prudent. As explained in Time magazine:16
“The risks of sun-related eye damage are greater at certain times of the day and in certain settings. Water, snow and car windshields can reflect light into the eyes, and spending time on a boat, around snow, or in a vehicle on a sunny day ‘is like getting a double dose of ultraviolet light,’ says Dr. C. Stephen Foster, a professor of ophthalmology at Harvard Medical School.
‘You’re getting the direct exposure from the sun and a second exposure from the reflected light.’ Also, at higher altitudes the sun’s rays are stronger, and the attendant eye risks increase. Wearing sunglasses can protect a person’s eyes from all these concerns.”
As noted by Time, when selecting a pair of sunglasses, the most important criteria is its ability to block UVA and UVB rays. Look for a pair that blocks 99% to 100% of both. The color and shade of the glasses are of no particular concern.
Polarization17 also has no impact on UV protection, but can be useful for preventing glare that impedes visibility, and can therefore be a good choice on the ski slope and on the water.
The size of the lenses, on the other hand, is a consideration, as larger lenses offer better UV protection than smaller ones. Goggle-style glasses are the best, offering close to 100% protection regardless of your head position and location of the sun in the sky.18
Other Reasons to Avoid Routine Wear of Sunglasses
Another reason to avoid the routine use of sunglasses, with the exception of intense UV and high-glare conditions, is that when you wear sunglasses you prevent your eyes from absorbing full-spectrum light required for the proper synchronization of your circadian rhythm.
The reason light is so important for this process is because it serves as the major synchronizer of your master clock. This master clock is a group of cells in your brain called the suprachiasmatic nuclei. As a group, these nuclei synchronize to the light-dark cycle of your environment, based on when light hits light-sensing photoreceptors in your eye.
You also have other biological clocks throughout your body, and those clocks subsequently synchronize to your master clock. When your master clock is “off,” your body has trouble functioning properly. Your mood and sleep in particular will tend to suffer,19 and depression and insomnia may become problems. As explained in the 2009 study, “Effect of Light on Human Circadian Physiology”:20
“The circadian system in animals and humans, being near but not exactly 24-hours in cycle length, must be reset on a daily basis in order to remain in synchrony with external environmental time.
This process of entrainment is achieved in most mammals through regular exposure to light and darkness … Studies have revealed, how the timing, intensity, duration, and wavelength of light affect the human biological clock.”
Researcher Dan Pardi discussed all of this at depth in our 2014 interview, featured in “How the Cycles of Light and Dark Affect Your Health and Well-Being.” To maintain and anchor your master clock, you want to get bright outdoor light exposure for 30 to 60 minutes each day, ideally first thing in the morning and/or at solar noon.
Personally, I avoid wearing sunglasses unless I’m skiing or boating, as I believe your eyes need to receive the full spectrum of light to function optimally, and sunglasses block out essential wavelengths of the light spectrum.
Instead of sunglasses, I wear a lightweight cap with a visor to protect my face and eyes from direct sunlight. This is typically all that is needed to protect your eyes from harsh, direct rays, while still allowing your eyes to benefit from the full spectrum of light.