Why We Should Cut Down on Salt Independently of Blood Pressure

If you put people on a low-salt diet, meaning only getting twice as much sodium as they need, as opposed to a usual salt diet where they’re getting five times more, you get a significant improvement in artery function. Lower salt begets better arterial function, suggesting heart-protective effects beyond just blood pressure reduction. Now, this was after dropping people’s salt intake by about a teaspoon a day for two weeks. What if you only dropped salt intake by a half teaspoon or so a day? You still get a significant improvement in artery function, and it happens within just two days of reducing one’s salt intake—or, even after a single meal. A high-salt meal, which is to say just a “typical amount of salt consumed in a commonly eaten meal, can significantly suppress [artery function] within 30 [minutes].” In my video Sodium and Arterial Function: A-Salting Our Endothelium, I show what happens 30, 60, 90, and 120 minutes after consuming a meal with just a pinch of salt in it versus eating the same meal, but made with a quarter teaspoon of salt rather than a pinch: a significant suppression of arterial function. Now, is this in addition to the spike in blood pressure from salt or because of the spike in blood pressure?

If you take people with normal blood pressure and give them a bowl of soup containing the amount of salt a regular meal might contain, their blood pressure goes up over the next three hours compared to the same soup with no added salt. Now, this doesn’t happen to everyone; this is just the average response. Some people are resistant to the effects of salt on their blood pressure. So what if you repeated the artery function experiment on them? You get a paper entitled (*spoiler alert*): “High dietary sodium intake impairs endothelium-dependent dilation in healthy salt-resistant humans.” Indeed, even in people whose blood pressure is unresponsive to salt intake, they still suffer significant suppression of their artery function. So, independent of any effects on blood pressure, salt hurts our arteries, and that harm begins within minutes of consumption for our major arteries and even our tiny blood vessels.

Using something called laser Doppler flowmetry, you can measure blood flow in the tiny vessels in our skin. In the video, you can see the measurement of blood flow at baseline. Now, to get the blood vessels to open up, they warmed the skin. The reason we may turn pink when we get into a hot bath is that the blood vessels in our skin are opening up, and that’s what happened: a big increase in blood flow with the warming. That was on the low-salt diet, however. A high-salt diet starts out the same, but after the same warming, there’s significantly less blood flow. The arteries just don’t seem to open up as well on a high-salt diet, unless you inject vitamin C into the skin. That seems to reverse the salt-induced suppression of blood vessel function. So if an antioxidant reverses the salt effect, then the way salt may be damaging our artery function is through oxidative stress, the formation of free radicals in our blood stream. But, how?

There’s an enzyme in our body that can detoxify a million free radicals per second (!), 24 hours a day, 7 days a week. But, compared to a low-salt diet, if we consume a normal-salt diet, we suppress the activity of this detoxifying powerhouse of an enzyme. That may help explain why our artery function is much lower on salt. With our antioxidant enzymes crippled by the salt, all the excess free radicals may be crippling our arteries. Mop up those extra free radicals by infusing vitamin C into the bloodstream, however, and artery function returns to normal. In contrast, on a low-salt diet, if you drip vitamin C into people’s veins, nothing happens because our antioxidant enzymes are already taking care of business and haven’t been shackled by the sodium of a normal-salt diet.

Whereas potassium, concentrated in fruits and vegetables, softens the cells that line our arteries and increases the release of nitric oxide that allows our arteries to relax, sodium in our blood stiffens the artery lining within minutes and reduces nitric oxide release. The more salt, the less nitric oxide is produced. Consume one salty meal, and not only does our blood pressure go up, but our arteries literally stiffen. That’s why we could figure out four thousand years ago that too much salt was bad for us. Maybe we don’t need a double-blind trial. Maybe we don’t need to follow people around for a decade. We may just have to feed someone a bag of potato chips and take their pulse.


My video Sodium and Arterial Function: A-Salting Our Endothelium is part of an extended video series on sodium, trying to set the record straight on the “controversy” manufactured by the processed food industries. Check out the other installments:

Other salt-related videos of interest include:

I touched on potassium in Preventing Strokes with Diet and Lowering our Sodium-to-Potassium Ratio to Reduce Stroke Risk, but I’m looking forward to doing a deep dive into the mineral when I get a chance.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

We Have Specific Fruit and Vegetable Receptors

According to a recent survey, the number of Americans adults who say they are eating ‘pretty much whatever they want’ is at an all-time high,” which unfortunately includes “too few fruits and vegetables,” as well as “too little variety.” Half of all fruit servings are taken up by just six foods: orange juice, bananas, apple juice, apples, grapes, and watermelons. Only five foods—iceberg lettuce, frozen potatoes, fresh potatoes, potato chips, and canned tomatoes—make up half of all vegetable servings. We’re not only eating too few fruits and veggies. We’re also missing out on the healthiest fruits, which are berries, and the healthiest vegetables, which are dark green leafies. The fruit and vegetable palette for our palate is sadly lacking.

Why does dietary diversity matter? As I discuss in my video Specific Receptors for Specific Fruits and Vegetables, different foods may affect different problems. Cabbage, cauliflower, broccoli, and Brussels sprouts are associated with lower risk of colon cancer in the middle and right side of our body, whereas risk of colon cancer further down on the left side of our body appears to be better lowered by carrots, pumpkins, and apples. So, “different F/V [fruits and vegetables] may confer different risks for cancer” of different parts of even the same organ.

Variety is the spice of life—and may prolong it. “Independent from quantity of consumption, variety in fruit and vegetable consumption may decrease lung cancer risk,” meaning if two people eat the same number of fruits and vegetables, the one eating a greater variety may be at lower risk.

It’s not just cancer risk. In a study of thousands of men and women, a greater quantity of vegetables and a greater variety may independently be beneficial for reducing the risk of type 2 diabetes. Even after removing the effects of quantity, “each different additional two item per week increase in variety of F&V [fruit and vegetable] intake was associated with an 8% reduction in the incidence of T2D [type 2 diabetes].” Why? Well, it “may be attributable to individual or combined effects of the many different bioactive phytochemicals contained in F&V. Thus, consumption of a wide variety of F&V will increase the likelihood of consuming” more of them.

“All the vegetables may offer protection…against chronic diseases,” but “[e]ach vegetable group contains a unique combination and amount of these [phytonutrients], which distinguishes them from other groups and vegetables within their own group.” Indeed, because “each vegetable contains a unique combination of phytonutriceuticals (vitamins, minerals, dietary fiber and phytochemicals), a great diversity of vegetables should be eaten…to get all the health benefits.”

Does it matter, though, if we get alpha-carotene or beta-carotene? Isn’t an antioxidant an antioxidant? No. “It has been shown that phytochemicals bind to specific receptors and proteins” in our bodies. For example, our body appears to have a green tea receptor—that is, a receptor for EGCG, which is a key component of green tea. There are binding proteins for the phytonutrients in grapes, onions, and capers. In my video The Broccoli Receptor: Our First Line of Defense, I talk about the broccoli receptor, for instance. Recently, a cell surface receptor was identified for a nutrient concentrated in apple peels. Importantly, these target proteins are considered indispensable for these plants foods to do what they do, but they can only do it if we actually eat them.

Just like it’s better to eat a whole orange than simply take a vitamin C pill, because, otherwise, we’d miss out on all the other wonderful things in oranges that aren’t in the pill, by just eating an apple, we’re also missing out on all the wonderful things in oranges. When it comes to the unique phytonutrient profile of each fruit and vegetable, it truly is like comparing apples to oranges.


This is one of the reasons I developed my Daily Dozen checklist of foods to incorporate into one’s routine. Download the free iPhone and Android apps, and be sure to watch my video Dr. Greger’s Daily Dozen Checklist.

I discuss how produce variety—not just quality and quantity—may be important in Apples and Oranges: Dietary Diversity and Garden Variety Anti-Inflammation, so I hope you’ll check them out. You can also learn more about why combining certain foods together may be more beneficial than eating them separately in Food Synergy.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

How to Treat Dry Eye Disease Naturally with Diet

One of the most common eye disorders, dry eye disease, causes irritation or discomfort, and can decrease functional vision, sometimes causing a dramatic deterioration in the quality of life. About five million Americans over age 50 suffer from moderate-to-severe dry eyes, and tens of millions more have mild or episodic manifestations of the disease, at a cost of more than $50 billion.

In terms of treatment, there are several drops and drugs that can help. We spend hundreds of millions of dollars on things like artificial tears, but currently there is no therapy available to actually fix the problem. If drugs don’t work, doctors can try plugging up the outflow tear ducts, but that can cause complications, such as plugs migrating and eroding into the face, requiring surgical removal. Alternatively, surgeons can just cauterize or stitch up the ducts in the first place.

There has to be a better way.

What about prevention? Dry eyes can be caused by LASIK surgery, affecting about 20-40% of patients six months after the operation. With a million LASIK procedures performed annually, that’s a lot of people, and sometimes the long-term symptoms can be severe and disabling.

There’s a long list of drugs that can cause it, including antihistamines, decongestants, nearly all the antidepressants, anticonvulsants, antipsychotics, anti-Parkinson’s drugs, beta-blockers, and hormone replacement therapy, as well as a few herbal preparations.

In the developing world, vitamin A deficiency can start out as dry eyes and then progress to becoming the leading cause of preventable childhood blindness. Vitamin A deficiency is almost never seen in the developed world, unless you do it intentionally. There was a report in the 1960s of a guy who deliberately ate a vitamin A-deficient diet, living off of bread and lime juice for five years, and his eyes developed vascularization and ulceration of the cornea, which you can see (if you dare) in my Treating Dry Eye Disease with Diet: Just Add Water? video. That was better than what happened to an unfortunate woman who was the member of a cult and tried to live off of brown rice and herbal tea: Her eyes literally melted and collapsed.

There are also a couple case reports of autistic children who refused to eat anything but French fries or menus exclusively comprised of bacon, blueberry muffins, and Kool-Aid, and became vitamin A deficient. A case in the Bronx was written up as vegan diet and vitamin A deficiency, but it had nothing to do with his vegan diet—the kid refused to eat vegetables, consuming only potato chips, puffed rice cereal with non-fortified soymilk, and juice drinks. “His parents lacked particular skill in overcoming the child’s tendency to avoid fruits and vegetables.”

A plant-based diet may actually be the best thing for patients with dry eye disease, those who wear contact lenses, and those who wish to maximize their tear secretions. People with dry eyes should be advised to lower protein, total fat, and cholesterol intake, and do the following:

  • increase complex carbohydrates;
  • increase vitamin A content (by eating red, orange, yellow, and dark green leafy vegetables);
  • increase zinc and folate intake (by eating whole grains, beans, and raw vegetables, especially spinach);
  • ensure sufficient vitamin B6 and potassium intake (by eating nuts, bananas, and beans);
  • ensure sufficient vitamin C intake (by eating citrus);
  • eliminate alcohol and caffeine;
  • reduce sugar and salt intake; and
  • consume six to eight glasses of water per day.

We know dehydration can cause a dry mouth, but could dehydration cause dry eyes? It may seem kind of obvious, but evidently it was never studied until recently. Is the answer to just drink more water? We know that those suffering from dry eye are comparatively dehydrated, so researchers figured that tear secretion decreases with progressive dehydration just like saliva secretion decreases and gives us a dry mouth. And indeed, as one gets more and more dehydrated, their urine concentrates and so does the tear fluid. But one can reverse that with rehydration, raising the exciting prospect that improving whole-body hydration by getting people to drink more water might bring relief for those with dry eyes. The researchers recommend eight cups of water a day for women and ten cups a day for men.


Find more on the importance of proper hydration in my How Many Glasses of Water Should We Drink a Day?, Does a Drink Of Water Make Children Smarter?, and Can Dehydration Affect Our Mood? videos.

To learn more on other topics related to eye health, check out:

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: