Some two million people around the world suffer from a serious degenerative eye disease that literally has no treatment at all beyond “cross your fingers and hope for the best.”

But if you’re suffering from the gradual — and ultimately total — loss of vision that marks retinitis pigmentosa, you don’t have to cross your fingers anymore.

New research led by Harvard University shows an easy way to stop this frightening condition in its tracks — and it’s not a new drug with side effects or an operation with risks.

It’s an ordinary vitamin mixed with a little bit of fish.

Three clinical trials show that megadoses of vitamin A — 15,000 IU a day — combined with 0.2 grams a day of omega-3 fatty acids can slow the loss of vision by between 40 percent and 50 percent.

In real numbers, that could add up to an extra 18 years of vision.

The researchers don’t know for sure why roughly two servings of fatty fish a week can have such a powerful impact on all that vitamin A, but they’ve got their eyes on one omega-3 fatty acid in particular: DHA.

Your retina is already loaded with DHA (which is why fatty fish — not carrots — is what you should be eating for good vision even if you’re healthy). And in the case of retinitis pigmentosa, the researchers believe extra DHA is needed to help carry the vitamin A from the photoreceptor cells that have it to those that don’t.

The result isn’t a cure for retinitis pigmentosa, but it could dramatically change the prognosis.

Right now, someone with this condition can expect to go blind by the age of 60. With vitamin A and fish oil, that might be delayed until they’re almost 80 — or right around our actual life expectancy these days.

Since too much vitamin A can interfere with vitamin D and may even increase your risk of osteoporosis, don’t try treating yourself on this one — talk to your doctor about the best and safest way to raise your A levels.

And don’t forget to add the fish oil — because along with helping to slow retinitis pigmentosa, omega-3 fatty acids can also slash your risk of both the “wet” and “dry” forms of macular degeneration.

Fish oil isn’t just the best natural way to fight the ravages of heart disease — it’s also the best way to avoid problems with your ticker in the first place.

We’ve known all along that people who eat the most fatty fish have a lower risk of heart disease. And now, researchers say the omega-3 fatty acids found in those fish can also slash the odds of another serious heart problem: atrial fibrillation.

That’s a frightening — and all-too-common — condition where your heart loses its rhythm and starts galloping off like a spooked horse. People who have it say it can feel like your heart is getting ready to bounce right out of your chest.

But now, researchers say their study of more than 3,300 seniors who were tracked for 14 years found that those with the highest blood levels of omega-3 fatty acids — especially DHA — were 30 percent less likely to come down with the condition.

This isn’t the first study of its kind — others have also found that omega-3 fatty acids can slash the risk of A-fib, including an 18-year study out of Finland that found high levels cut that risk by 35 percent.

When you consider how many patients are fighting this disease, that’s a big deal.

Close to 10 percent of seniors eventually develop atrial fibrillation — and because the condition comes with a higher risk of stroke and heart failure, it’s often treated with the same risky blood-thinning meds given to heart patients.

There’s even one new blood thinner supposedly aimed just at A-fib patients — and that one could be even more dangerous than those other bad meds.

If fish oil can help you avoid the disease in the first place, I say load up now. After all, A-fib isn’t the only condition omega-3s can fight or prevent.

Studies have shown that omega-3 fatty acids can help the heart, brain, eyes and even gums. One recent study even links fish oil to a lower risk of colon polyps in women.

This stuff is so good that even Big Pharma wants in — so you’re starting to see expensive prescription omega-3 blends on the market.

Save your money — a quality omega-3 supplement from a trusted vitamin maker is all you and your heart really need.

Gentlemen, if you want to keep your sperm swimming — and who doesn’t? — head on over to the nearest fish market and load up on tuna and salmon.

The fattier the fish, the better — because the same fatty acids that make these fish such healthy choices for everything from your heart to your eyes to your brain are also positively critical to your fertility.

The omega-3 fatty acid docosahexaenoic acid (DHA) is one of the essential building blocks of sperm — and a new study on mice shows how it’s also a key part of the acrosome, which is what enables the sperm to penetrate the egg.

You might say it’s the most important part of all. The mice would agree: When they were denied DHA, they produced fewer sperm — and the ones they did create were misshapen, rendering them infertile.

But once DHA was put back into their diets, they began to produce again like, well, mice. (Side note: There has to be a pest-control angle in here somewhere).

This is, of course, just one study on mice. But human studies have also shown how high levels of these essential fatty acids can boost your fertility.

One study from just a couple of years back found that fertile men tended to have higher blood levels of omega-3 fatty acids, while infertile men had higher levels of omega-6 fatty acids.

And these days, with diets heavy in grain fed animals from factory farms, most of us get less of the desirable omega-3s and far more of the undesirable omega-6 fatty acids.

Call it one more reason to switch to fresh all-natural grass-fed meats.

Naturally, omega-3 fatty acids aren’t the only answers for sperm health. A lot goes into male fertility — and studies over the years have shown that high levels of vitamin D can boost the speed and forward motion of sperm, an essential trait called motility.

Other studies have also shown that junk food, soda and the BPA used to line canned goods (including soda cans) can slash sperm levels and turn the ones that are left into the microscopic equivalent of couch potatoes: slow, lazy and uninterested in the quest for the egg.

That would explain the recent rise in male infertility.

“Fish is brain food” is the kind of age-old folk wisdom that’s been proven time and again by cutting-edge science — and the latest research confirms that the best way to keep your brain swimming in gray matter is with a steady diet of fish.

I mean that literally: Seniors who eat fish at least once a week have more of that critical gray matter, giving them a lower risk of dementia and Alzheimer’s disease.

The biggest boost is in the frontal and temporal lobes — specifically the areas most closely linked to memory and learning, or exactly where you want your extra gray matter to be.

And if you think the benefits inside the brain are impressive, you should see how that translates out in the real world: Just 3.2 percent of the fish-eaters developed cognitive decline over five years, versus 30.8 percent of those who ate little to no fish, according to data presented at a Radiological Society of North America meeting.

If there’s one area where the researchers found no benefit, it was in fried fish — and I have to wonder if it’s because of the frying… or because of the oils people tend to fry things in.

Most people don’t fry their foods — fish or otherwise — in healthy oils. They fry them in the unhealthiest polyunsaturated oils of all, including blended vegetable oils, soybean oil and safflower oil.

Try a healthier oil — like peanut oil — and all your fried foods will get a health boost (and taste better, too).

But let’s get back to seafood, cooked however you like — because a diet rich in fatty fish will do so much more than protect your brain. Fatty fish can help prevent heart disease, protect your vision, beat depression and even improve your gums.

Yet despite all those benefits, some simply won’t eat fish to save their lives. Maybe it’s the smell… the taste… the texture… or all three.

Whatever the reason, you don’t have to actually eat any fish at all to get the benefits — because almost all of those benefits come from the omega-3 fatty acids found in fish oil, which you can find almost anywhere as a supplement.

Shop around before you commit to one — some brands will leave you with the “fish burps,” which is a little counterproductive if you’re taking pills to avoid the taste of fish in the first place.

Buy smaller sizes or sample packs first — it might take a little trial-and-burping, but eventually, you’ll find one that works for you.