Dear Mark: Sun Exposure and Eyesight; Vasectomies

EyeFor today’s edition of Dear Mark, we’ve got a quick two-parter. First, I discuss the pros and cons of ocular sunlight exposure in children (and adults). Should kids leave the house with a pair of wraparound goggles every single time, or are their prepubescent eyes safe without them? If too much sun exposure is bad, is none the best? Then, we cover the pros and cons of getting a vasectomy. Are there real health risks, like increased chances of cancer and/or heart disease? Will you lose functionality down there and experience a drop in testosterone?

Let’s go:

Dear Mark,

The linked WSJ article seems a tad overblown with respect to the risks the sun poses to kids eyes. Would love to get your take.

It’s very similar to the conventional wisdom on sun exposure for skin: less is better, all the way to zero. In my view, that simply can’t be optimal for humans.

I’ve got three girls. Should I be sending out into the world with sunglasses, always??


It depends.

While I’m definitely a fan of the sun and regular sun exposure, and I agree that the article is pretty alarmist, there are real issues with too much sun exposure to the eye:

Photokeratitis – Temporary inflammation of the cornea from excessive UV radiation. This is basically a corneal sunburn. Painful but reversible and doesn’t seem to cause any long term complications. Snow-farers know it as snow blindness because the highly reflective snow amplifies the UV. The Inuit even made snow goggles from caribou antlers, cutting slits that allowed just enough light to see without causing snow blindness.

Pterygium – Mostly cosmetic, a pterygium is a blemish along the conjunctiva (the thin layer lining the white of the eye) that can become irritated and inflamed. Evidence shows that UV exposure is a likely risk factor, with outdoor postal workers experiencing higher rates of the condition.

Cataract – The leading cause of blindness, cataracts form when proteins in the lens unravel, become entangled, and absorb pigment that then increasingly obscures the vision. Ocular UVB exposure is a risk factor for cataract formation, which is why French mountain guides – who are constantly outside during the day without much respite – have far more cataract formation and surgery than non-guides.

Overall I’m with you, James. Sunlight is a reality of the outside world and unavoidable if you’re outside; we are creatures of the outdoors. We’ve established that moderate amounts of sunlight are definitely good for our skin and our overall health, and it’s difficult to fathom that going outside for an hour or two without judiciously slapping a pair of Blue Blockers on immediately would place our eyesight in mortal danger. Too much? Sure, that’s true for most stimuli, let alone the light from a massive ball of cosmic energy illuminating. But a normal, sane amount? Given the ubiquity of sunlight in the natural environment and the fact that we’ve evolved in said environment, it seems implausible that any modicum of sunlight is dealing major damage to our eyes.

There may also be benefits to unfiltered ocular sun exposure. We often talk about the dangers of excessive light at night disrupting your sleep by inhibiting melatonin secretion. Well, the opposite happens when you get it during the day: it wakes you up and establishes (or maintains) a healthy, natural circadian rhythm. If you’re always avoiding full spectrum, truly bright daytime light, your rhythm will be off. And sure enough, people who get the most light during the morning and daytime begin producing melatonin earlier in the evening. There’s nothing better than full on sunlight to provide that.

Is there a time for sunglasses? Yes, just as a good UVA-and-UVB-blocking zinc oxide sunscreen can come in handy when you know you’re going to be out in the sun without shade for longer than you and your skin would prefer, a pair of sunglasses that block both UVA and UVB can help protect your eyes in the same situation. Doubly so if you’re in the snow, on a body of water, or at the beach where the power of UV is reflected and magnified; glasses are a good option to have in these situations. I wear ’em myself – just not all the time.

I would provide sunglasses for your girls, not force them. As the pediatric opthomologist in the article even mentions, it’s better to run around and play outside without sunglasses than sit inside and watch TV. Besides, your kids are probably eating nutrient-dense, antioxidant-rich food, and that’s protective of the eye against sunlight damage. A smart, sane position is to get some sunlight directly in your eyes each day. Not a huge amount. Don’t stare into the sun on purpose or anything silly like that. Just go outside without sunglasses on (but handy in case you need them), go about your business, and the light will come to you.


My wife and I are done having kids, but we’re also done with condoms and birth control. Neither of us can stand either, so I’m thinking hard about getting a vasectomy. Is there anything I should know? Are there any dangers associated with the procedure and the aftermath? I want everything else to work as intended, ya know?



Good news, Tim. The evidence strongly suggests that your facilities will remain fully operational, your sex life will improve (or at least stay the same), and your testosterone levels will be unaffected. All they’re doing is capping the vas deferens – the tubes that deliver sperm during ejaculation. You can still ejaculate, and the “body” is none the wiser. You’re just “inactive.”

  • In one 2005 study of 64 men about to undergo vasectomy surgery, researchers analyzed their sexual function pre-op and 90 days post-op. 67% of the men improved their function after surgery, while 17% worsened and 16% remained constant. Another study found that roughly a third of men enjoyed improved sexual function after vasectomy, while nearly 50% remained unchanged. The results differ across other studies, but for the most part the vast majority of men enjoy improved or unchanged sexual function after getting a vasectomy. If you’re happy with your work now, you’ll be fine.
  • Vasectomy seems to increase sexual satisfaction among couples as well. Husbands who received vasectomies and wives who received husbands who received vasectomies both reported improved sex, with the women enjoying the biggest increases in satisfaction. 93% of the males and 97% of the females would “recommend and do vasectomy again,” such were the benefits.
  • Rats who get the snip have similar testosterone profiles as intact rats. Although no human data exists, the fact that erection function and sexual satisfaction usually either increase or stay the same in post-op men indicates that testosterone is unaffected.

Associations between vasectomies and various health risks have been proposed, however.

Heart disease: There were very faint inklings of a connection between the two, but recent evidence has ruled it out.

Cancer: Much the same story as heart disease. Suspicion has made way for exoneration. Testicular cancer? No connection.

You might have seen the reports of a new study showing a link with prostate cancer. That’s true, and the headlines are scary. But consider that men who’ve had a vasectomy are probably more frequent visitors to the urologist than intact men. They’ll be receiving more tests in general and there will be more opportunities to take prostate cancer tests. Even still, the increase in absolute risk potentially caused by vasectomy remains low.

Sex with a loved partner is very important for many people. And on a physiological level, it’s extremely healthy. If this vasectomy will help you have more and better and less stress-free sex with your wife, it’s absolutely worth the very slight potential increase in prostate cancer risk. Go for it.

Thanks for reading, all. Let’s hear what you have to say about all this in the comments!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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