Spinach, Oxalates, Calcium, and Vitamin A toxicosis

[PBluejay2]

I fear this might cause some controversy because it contradicts some of our long-held assumptions/beliefs (the world is not flat?), but I've been questioning some of our "givens" (questioning minds never stop) and did some research in the USDA and other databases regarding a couple of nutrition issues. I found no where that the oxalates in spinach or any other food blocks the absortion of the calcium contained in any other food. I also tried to confirm that animals (humans included) have been known to get vitamin A toxicosis from vegetables and found nothing. To confirm or refute my findings, I emailed a Phd in nutrition. Below is our exchange:

My inquiry:

I rehabilitate squirrels, and certain issues about their diets have come up. My questions are

1) Do the oxalates in spinach block calcium absorption from any other foods or only the calcium in the spinach itself?
2) Can an animal (human even) get Vitamin A toxicosis from eating vegetables high in vitamin A? I read about some mountain climbers getting vitamin A toxicosis from eating a diet consisting primarily of bear liver (of all things), but veggies?

Her response (my bold):

Oxalates reduce the absorption of the minerals in the food itself (calcium and iron primarily) because they chemically bind the mineral in the food so it’s not absorbed. Other food sources without oxalates will not be affected.

The active form of Vitamin A is found in animal products like liver… polar bear liver has the most but regular old beef liver has 6580 micrograms/3 oz and upper tolerable level (to avoid toxicity) is 3000. The RDA for humans is 700-900. The plant version is a precursor form of Beta Carotene. There is no possibility of toxicity with plant sources because the liver will not convert it fast enough to be toxic and the excess carotene is stored in the fat cells under the skin and causes the skin to become “orangy”.

[4skwerlz]

Oxalates can block the calcium in any food with which they are eaten. For example, if you drink tea with milk, the oxalates in the tea will block most of the calcium in the milk. If one were attempting to feed a mix of high-calcium/low-phosphorus vegetables, adding spinach to the bowl hardly seems the healthiest option. Even if there is only enough oxalate in spinach to block the amount of calcium in the spinach, there's still the phosphorus in the spinach, which would now have no calcium to bind with. I guess the point is, anything that blocks calcium hardly seems like the healthiest veggie possible with our MBD-prone critters. Plus, the concern about the formation of crystals or stones in the kidneys and bladder remains.

As for vitamin A, first of all, vitamin overdoses in humans other than through oversupplementation are rare. In small animals however, there is more danger: they eat 10 times more food relative to their own body weight than a human. Picture eating 15 pounds of healthy foods per day and you might start to get those vitamin levels up there.

However, my main concern with frank vitamin A toxicosis is, of course, with fortified foods and vitamin supplements designed for birds since they contain large amounts of vitamin A, and it's almost never the nontoxic, natural form (beta-carotene), but rather the much more toxic (and cheaper) retinoids.

Although HHBs are made with mostly beta-carotene, other rodent blocks contain retinoids--often at very high doses. So the idea behind limiting high vitamin A veggies is simply to keep all the nutrients in balance, understanding that different brands of rodent block may be fed. And in any case, we certainly don't want our squirrels turning orange!

That being said, the Healthy Diet is super-conservative, admittedly. And I'm sure some of the "rules" there could be broken without harm.

[PBluejay2]

Oxalates will block the calcium in any food with which they are eaten. For example, if you drink tea with milk, the oxalates in the tea will block most of the calcium in the milk.

Yes, I read what the nutritionist at the Mayo clinic said about milk and tea, and I can't speak to that (but I don't feed my squirrels either milk or tea), but I researched and asked specifially about the oxalates in vegetables blocking calcium absorption, and from what I could find (and was told), it blocks the absoption of the calcium in the vegetable itself, not the calcium in any other food. That's why spinach, for example, is high in calcium but only 5% (I think) of it is absorbed.

I quote: "although spinach has a lot of calcium, it also contains a substance -- oxalic acid -- that binds up its calcium and prevents absorption of all but about 5 percent of it. However, the oxalic acid in spinach and foods like rhubarb does not interfere with absorption of calcium from other foods eaten at the same time."

I looked on several databases to find concrete evidence to the contrary and consulted a Phd with 35 years of researching and teaching nutrition, but if you have evidence to the contrary, I'll present it to her.

If one were attempting to feed a mix of high-calcium/low-phosphorus vegetables, adding spinach to the bowl would certainly work against that.

I don't understand this. Spinach has a 2.0 to 1 Calcium to Phosphorus ratio (99 mg Ca to 49 mg Phos per 100 gms). And if the oxalic acid affects only the calcium in the spinach, then for every 100 grams of spinach, the squirrels would still be getting 5 mg of calcium to the good.

I suppose one could advise folks to feed spinach as a separate meal, but that starts to get complicated. Plus, the concern about the formation of crystals or stones in the kidneys and bladder remains.

Yes, too much oxalate can cause kidney stones and crystals in the urine, but so can too much calcium. From what I've read, it's often the result of a Ph imbalance. Oxalic acid is an acid (obviously) and calcium is a base.

As for vitamin A, first of all, vitamin overdoses in humans other than through oversupplementation are rare. In small animals however, there is more danger: they eat 10 times more food relative to their own body weight than a human. Picture eating 15 pounds of healthy foods per day and you might start to get those vitamin levels up there.

Yes, but if you go on that logic, they're eating 10 times more of EVERYTHING--all vitamins, minerals, amino acids, fats (the idea that they consume their body weight a week is another question I want to research one day. I've read that it requires a pound of "mast" a week for them, but I haven't found evidence yet what percentage of that mast they actually eat). Obviously they are different than we are--their metabolisms and requirements. You could make that same argument for ANY nutritional element. The key word you used was "oversupplementation." I don't consider providing squirrels with a variety of veggies--some high in Vitamin A, some not--"supplementation." ADDING vitamins to a natural diet is supplementation--overdone or not.

However, my main concern with frank vitamin A toxicosis is, of course, with fortified foods and vitamin supplements designed for birds since they contain large amounts of vitamin A, and it's almost never the nontoxic, natural form (beta-carotene), but rather the much more toxic (and cheaper) retinoids.

I think any doctor or nutritionist would agree that the BEST way to get the necessary vitamins and minerals one needs is through natural foods. From what I've read, Vitamin A toxicosis has occurred primarily through gross oversupplementation. All blocks, including HHBs (and your blocks aren't the issue!), are supplemented with processed vitamins. Quite frankly, since so many foods have Vitamin A in them, and to use your argument, squirrels eat 10 times the food we do per body weight, I wonder why you supplement it (Vit A) at all if one feeds his or her squirrel a variety of vegetables (including the green, yellow, and orange) a week.

Although HHBs are made with mostly beta-carotene, other rodent blocks contain retinoids--often at very high doses. So the idea behind limiting high vitamin A veggies is simply to keep all the nutrients in balance, understanding that different brands of rodent block may be fed. And in any case, we certainly don't want our squirrels turning orange!

Ha! No orange squirrels for me! (But I do have three in my yard with orange tails--think there's a connection?). But again, the point was that they won't get Vitamin A toxicosis from the veggies. I'm sure you put the best quality/healthiest supplements in your HHBs, but again, why supplement something artificially that doesn't need supplementing if the squirrels can get it naturally?

That being said, the Healthy Diet is super-conservative, admittedly. And I'm sure some of the "rules" there could be broken without harm.

It's not the "rules" to be "broken" that's the issue, IMHO, but the possibility that the "rules" were made on the basis of inaccurate information"

[4skwerlz]

The Healthy Diet is always open to improvement. If you have changes to suggest, then by all means do so.

[crazysquirrels]

My Jackie is very healthy and been on your squirrel diet since day 1. I know it could be changed but its not really broken, right.

[PBluejay2]

My Jackie is very healthy and been on your squirrel diet since day 1. I know it could be changed but its not really broken, right.

I didn't post this information to change anything necessarily, or to suggest there's anything "unhealthy" about the "Healthy Diet," but I think we can relax a little bit about what veggies and how much we can feed them. There was a recent post about kale wherein the poster was encouraged to limit kale (high in calcium) because of Vitamin A. This initiated my inquiry since I give my squirrels both kale and collards every day (not that they eat them every day). Since my findings are that Vitamin A in vegetables cannot cause toxicosis (at worst orange skin) as was previously believed, and they won't OD on it, I feel better about the diet I offer. We might also want to rethink spinach, especially since from what I've read doctors and nutritionists believe that the other nutrients in it are of enough benefit that they outweigh the fact that there may not be much absorbable calcium in it and the oxalates in it do not block calcium contained in other foods. Face it, if we're warned against feeding too much yellow and orange and now dark green veggies (those highest in calcium), that really puts a limit on our choices. I'm all for feeding rodent blocks, and will most certainly continue to feed them myself, but in my view they are a vehicle for ensuring the squirrels get their vitamins and minerals (and, arguably, some protein). I believe there are other ways to ensure this, and until I see little bistros out in the wild that squirrels frequent to get blocks, I will continue to believe so. By and large, the cases of MBD and other nutritional problems we have seen have been cases where the owners had no clue about what to feed their pets and were feeding diets that were limited to either junk (crackers and Peanut M&Ms) and/or diets that were WAY unbalanced as far as calcium and phosphorus (corn, sunflower seeds, nuts).

Once again, my intent was not to suggest that there is anything "wrong" with the "Healty Diet" as it exists. I fully understand that it's difficult for some to rethink the "givens" and venture outside of what they think is "the known," but I am of a mind that, even though something may "work" and not necessarily need "fixing," that doesn't mean it can't be improved or that it is beyond questioning. I have my own ideas about nutrition, some of which may not be what is currently commonly accepted, and will present them when I am ready, but until then I will share what I find concerning specific foods so that our squirrels might enjoy a more varied and natural diet.

[4skwerlz]

Sorry, it was time for my nap.

About vitamin A, just to recap, here are the concerns:

1. We are talking about concentrations of one nutrient (beta-carotene) at extremely high levels: currently around 700% of the recommended amount, and I guess the proposed increase would push it well into the 2000% range. When retinoid intake is adequate (as it would be with the healthy diet), all of this beta-carotene would be "excess" which means it would be stored in the fat. This can cause you to turn orange. In humans, that can occur at 10X recommended levels. This also seems, on the face of it, to violate the principle of a "balanced diet."

2. Though not actually toxic, beta-carotene does interact and interfere with the absorption of other nutrients. For example, the various carotenids all compete with one another. High beta-carotene intake suppresses lycopene, which is vital for eye health, and its function cannot be replaced by beta-carotene. Beta-carotene also plays a role in bone-building, and at least one study found high intake associated with osteoporosis in humans (this is not conclusive by any means of course; it's just one study that I know of). And it is better established that beta-carotene interferes with vitamin E absorption. This has been found specifically in rats (i.e., tissue concentrations of vit E were half the normal level when given excess beta-carotene), which is concerning, at least to me. Vit A is abundant in foods; vitamin E much less so.

3. Some of the high-vit-A foods are also quite energy dense, such as sweet potato. So in that case, there are two areas of concern.

4. Dr. Calvert asserted that these foods should never be fed to squirrels.

I like to err on the side of caution, always. I know that personally, I would limit these foods for my own squirrel, but the issue is whether we're going to change or remove the limits on the Healthy Diet.

And frankly, I'm curious why the huge "pro vitamin A" push?

[PBluejay2]

Sorry, it was time for my nap.

About vitamin A, just to recap, here are the concerns:

1. We are talking about concentrations of one nutrient (beta-carotene) at extremely high levels: currently around 700% of the recommended amount, and I guess the proposed increase would push it well into the 2000% range. When retinoid intake is adequate (as it would be with the healthy diet), all of this beta-carotene would be "excess" which means it would be stored in the fat. This can cause you to turn orange. In humans, that can occur at 10X recommended levels. This also seems, on the face of it, to violate the principle of a "balanced diet."

2. Though not actually toxic, beta-carotene does interact and interfere with the absorption of other nutrients. For example, the various carotenids all compete with one another. High beta-carotene intake suppresses lycopene, which is vital for eye health, and its function cannot be replaced by beta-carotene. Beta-carotene also plays a role in bone-building, and at least one study found high intake associated with osteoporosis in humans (this is not conclusive by any means of course; it's just one study that I know of). And it is better established that beta-carotene interferes with vitamin E absorption. This has been found specifically in rats (i.e., tissue concentrations of vit E were half the normal level when given excess beta-carotene), which is concerning, at least to me. Vit A is abundant in foods; vitamin E much less so.

3. Some of the high-vit-A foods are also quite energy dense, such as sweet potato. So in that case, there are two areas of concern.

4. Dr. Calvert asserted that these foods should never be fed to squirrels.

I like to err on the side of caution, always. I know that personally, I would limit these foods for my own squirrel, but the issue is whether we're going to change or remove the limits on the Healthy Diet.

And frankly, I'm curious why the huge "pro vitamin A" push?

It's not a "pro vitamin A push." It's a push not to limit foods because of bad information. I think the greater variety we offer the better. Please include your sources when you borrow info.

[4skwerlz]

It's not a "pro vitamin A push." It's a push not to limit foods because of bad information. I think the greater variety we offer the better. Please include your sources when you borrow info.

Which of this information is bad?

[PBluejay2]

Which of this information is bad?

“Avoid spinach; it is high in oxalates, which can block calcium absorption.” (unless you're talking about the calcium IN the spinach)


“**Very high in Vit. A. Don’t feed more than one tablespoon per month to avoid toxicity.”

[4skwerlz]

“Avoid spinach; it is high in oxalates, which can block calcium absorption.” (unless you're talking about the calcium IN the spinach)

Well it does block the calcium in the spinach, all but about 5% of it. Leaving a true calc/phos ratio of 1:10, hardly a healthy ratio. And I thought you were the one who was so focused on the ratios?

Spinach has long been believed to be a good calcium source in a squirrel's diet; many rehabbers still believe it. It's been a hard slog to get rid of that idea. So I thought it was important to not just eliminate spinach from the list, but to explain that it is not a good calcium source.

“**Very high in Vit. A. Don’t feed more than one tablespoon per month to avoid toxicity.”

Is THAT your beef? Well, I suppose it could say "to avoid excessive intake" or "to avoid interfering with absorption of other nutrients." Would that be better?