Several commenters have asked for my opinion on recent statements by prominent health researchers that many Americans are suffering from unrecognized vitamin A toxicity. Dr. John Cannell of the Vitamin D Council is perhaps the most familiar of them. Dr. Cannell's mission is to convey the benefits of vitamin D to the public. The Vitamin D Council's website is a great resource.
Vitamin A is a very important nutrient. Like vitamin D, it has its own nuclear receptors which alter the transcription of a number of genes in a wide variety of tissues. Thus, it is a very fundamental nutrient to health. It's necessary for proper development, vision, mineral metabolism, bone health, immune function, the integrity of skin and mucous membranes, and many other things. Vitamin A is a fat-soluble vitamin, and as such, it is possible to overdose. So far, everyone is in agreement.
The question of optimal intake is where opinions begin to diverge. Hunter-gatherers and healthy non-industrial cultures, who almost invariably had excellent dental and skeletal development and health, often had a very high intake of vitamin A (according to Dr. Weston Price and others). This is not surprising, considering their fondness for organ meats. A meager 2 ounces of beef liver contains about 9,500 IU, or almost 200% of your U.S. and Canadian recommended daily allowance (RDA). Kidney and eye are rich in vitamin A, as are many of the marine oils consumed by the Inuit and other arctic groups.
If we can extrapolate from historical hunter-gatherers, our ancestors didn't waste organs. In fact, in times of plenty, some groups discarded the muscle tissue and ate the organs and fat. Carnivorous animals often eat the organs first, because they know exactly where the nutrients are. Zookeepers know that if you feed a lion nothing but muscle, it does not thrive.
This is the background against which we must consider the question of vitamin A toxicity. Claims of toxicity must be reconciled with the fact that healthy cultures often consumed large amounts of vitamin A without any ill effects. Well, you might be surprised to hear me say that I do believe some Americans and Europeans suffer from what you might call vitamin A toxicity. There is a fairly consistent association between vitamin A intake and bone mineral density, osteoporosis and fracture risk. It holds true across cultures and sources of vitamin A. Chris Masterjohn reviewed the epidemiology here. I recommend reading his very thorough article if you want more detail. The optimum intake in some studies is 2-3,000 IU, corresponding to about 50% of the RDA. People who eat more or less than this amount tend to suffer from poorer bone health. This is where Dr. Cannell and others are coming from when they say vitamin A toxicity is common.
The only problem is, this position ignores the interactions between fat-soluble vitamins. Vitamin D strongly protects agains vitamin A toxicity and vice versa. As a matter of fact, "vitamin A toxicity" is almost certainly a relative deficiency of vitamin D. Vitamin D deficiency is also tightly correlated with low bone mineral density, osteoporosis and fracture risk. A high vitamin A intake requires vitamin D to balance it. The epidemiological studies showing an association between high-normal vitamin A intake and reduced bone health all sported populations that were moderately to severely vitamin D deficient on average. At optimal vitamin D levels, 40-70 ng/mL 25(OH)D, it would take a whopping dose of vitamin A to induce toxicity. You might get there if you eat nothing but beef liver for a week or two.
The experiment hasn't been done under controlled conditions in humans, but if you believe the animal studies, the optimal intake for bone mineral density is a high intake of both vitamins A and D. And guess what? A high intake of vitamins A and D also increases the need for vitamin K2. That's because they work together. For example, vitamin D3 increases the secretion of matrix Gla protein and vitamin K2 activates it. Is it any surprise that the optimal proportions of A, D and K occur effortlessly in a lifestyle that includes outdoor activity and whole, natural animal foods? This is the blind spot of the researchers who have warned of vitamin A toxicity: uncontrolled reductionism. Vitamins do not act in a vacuum; they interact with one another. If your theory doesn't agree with empirical observations from healthy cultures, it's back to the drawing board.
High-vitamin cod liver oil is an excellent source of vitamins A and D because it contains a balanced amount of both. Unfortunately, many brands use processing methods that reduce the amount of one or more vitamins. See the Weston Price foundation's recommendations for the highest quality cod liver oils. They also happen to be the cheapest per dose. I order Green Pasture high-vitamin cod liver oil through Live Superfoods (it's cheaper than ordering directly).
So is vitamin A toxicity a concern? Not really; the concern is vitamin D deficiency.
Is Vitamin A Toxicity a Concern?
Several commenters have asked for my opinion on recent statements by prominent health researchers that many Americans are suffering from unrecognized vitamin A toxicity. Dr. John Cannell of the Vitamin D Council is perhaps the most familiar of them. Dr. Cannell's mission is to convey the benefits of vitamin D to the public. The Vitamin D Council's website is a great resource.
Vitamin A is a very important nutrient. Like vitamin D, it has its own nuclear receptors which alter the transcription of a number of genes in a wide variety of tissues. Thus, it is a very fundamental nutrient to health. It's necessary for proper development, vision, mineral metabolism, bone health, immune function, the integrity of skin and mucous membranes, and many other things. Vitamin A is a fat-soluble vitamin, and as such, it is possible to overdose. So far, everyone is in agreement.
The question of optimal intake is where opinions begin to diverge. Hunter-gatherers and healthy non-industrial cultures, who almost invariably had excellent dental and skeletal development and health, often had a very high intake of vitamin A (according to Dr. Weston Price and others). This is not surprising, considering their fondness for organ meats. A meager 2 ounces of beef liver contains about 9,500 IU, or almost 200% of your U.S. and Canadian recommended daily allowance (RDA). Kidney and eye are rich in vitamin A, as are many of the marine oils consumed by the Inuit and other arctic groups.
If we can extrapolate from historical hunter-gatherers, our ancestors didn't waste organs. In fact, in times of plenty, some groups discarded the muscle tissue and ate the organs and fat. Carnivorous animals often eat the organs first, because they know exactly where the nutrients are. Zookeepers know that if you feed a lion nothing but muscle, it does not thrive.
This is the background against which we must consider the question of vitamin A toxicity. Claims of toxicity must be reconciled with the fact that healthy cultures often consumed large amounts of vitamin A without any ill effects. Well, you might be surprised to hear me say that I do believe some Americans and Europeans suffer from what you might call vitamin A toxicity. There is a fairly consistent association between vitamin A intake and bone mineral density, osteoporosis and fracture risk. It holds true across cultures and sources of vitamin A. Chris Masterjohn reviewed the epidemiology here. I recommend reading his very thorough article if you want more detail. The optimum intake in some studies is 2-3,000 IU, corresponding to about 50% of the RDA. People who eat more or less than this amount tend to suffer from poorer bone health. This is where Dr. Cannell and others are coming from when they say vitamin A toxicity is common.
The only problem is, this position ignores the interactions between fat-soluble vitamins. Vitamin D strongly protects agains vitamin A toxicity and vice versa. As a matter of fact, "vitamin A toxicity" is almost certainly a relative deficiency of vitamin D. Vitamin D deficiency is also tightly correlated with low bone mineral density, osteoporosis and fracture risk. A high vitamin A intake requires vitamin D to balance it. The epidemiological studies showing an association between high-normal vitamin A intake and reduced bone health all sported populations that were moderately to severely vitamin D deficient on average. At optimal vitamin D levels, 40-70 ng/mL 25(OH)D, it would take a whopping dose of vitamin A to induce toxicity. You might get there if you eat nothing but beef liver for a week or two.
The experiment hasn't been done under controlled conditions in humans, but if you believe the animal studies, the optimal intake for bone mineral density is a high intake of both vitamins A and D. And guess what? A high intake of vitamins A and D also increases the need for vitamin K2. That's because they work together. For example, vitamin D3 increases the secretion of matrix Gla protein and vitamin K2 activates it. Is it any surprise that the optimal proportions of A, D and K occur effortlessly in a lifestyle that includes outdoor activity and whole, natural animal foods? This is the blind spot of the researchers who have warned of vitamin A toxicity: uncontrolled reductionism. Vitamins do not act in a vacuum; they interact with one another. If your theory doesn't agree with empirical observations from healthy cultures, it's back to the drawing board.
High-vitamin cod liver oil is an excellent source of vitamins A and D because it contains a balanced amount of both. Unfortunately, many brands use processing methods that reduce the amount of one or more vitamins. See the Weston Price foundation's recommendations for the highest quality cod liver oils. They also happen to be the cheapest per dose. I order Green Pasture high-vitamin cod liver oil through Live Superfoods (it's cheaper than ordering directly).
So is vitamin A toxicity a concern? Not really; the concern is vitamin D deficiency.
Vitamin A is a very important nutrient. Like vitamin D, it has its own nuclear receptors which alter the transcription of a number of genes in a wide variety of tissues. Thus, it is a very fundamental nutrient to health. It's necessary for proper development, vision, mineral metabolism, bone health, immune function, the integrity of skin and mucous membranes, and many other things. Vitamin A is a fat-soluble vitamin, and as such, it is possible to overdose. So far, everyone is in agreement.
The question of optimal intake is where opinions begin to diverge. Hunter-gatherers and healthy non-industrial cultures, who almost invariably had excellent dental and skeletal development and health, often had a very high intake of vitamin A (according to Dr. Weston Price and others). This is not surprising, considering their fondness for organ meats. A meager 2 ounces of beef liver contains about 9,500 IU, or almost 200% of your U.S. and Canadian recommended daily allowance (RDA). Kidney and eye are rich in vitamin A, as are many of the marine oils consumed by the Inuit and other arctic groups.
If we can extrapolate from historical hunter-gatherers, our ancestors didn't waste organs. In fact, in times of plenty, some groups discarded the muscle tissue and ate the organs and fat. Carnivorous animals often eat the organs first, because they know exactly where the nutrients are. Zookeepers know that if you feed a lion nothing but muscle, it does not thrive.
This is the background against which we must consider the question of vitamin A toxicity. Claims of toxicity must be reconciled with the fact that healthy cultures often consumed large amounts of vitamin A without any ill effects. Well, you might be surprised to hear me say that I do believe some Americans and Europeans suffer from what you might call vitamin A toxicity. There is a fairly consistent association between vitamin A intake and bone mineral density, osteoporosis and fracture risk. It holds true across cultures and sources of vitamin A. Chris Masterjohn reviewed the epidemiology here. I recommend reading his very thorough article if you want more detail. The optimum intake in some studies is 2-3,000 IU, corresponding to about 50% of the RDA. People who eat more or less than this amount tend to suffer from poorer bone health. This is where Dr. Cannell and others are coming from when they say vitamin A toxicity is common.
The only problem is, this position ignores the interactions between fat-soluble vitamins. Vitamin D strongly protects agains vitamin A toxicity and vice versa. As a matter of fact, "vitamin A toxicity" is almost certainly a relative deficiency of vitamin D. Vitamin D deficiency is also tightly correlated with low bone mineral density, osteoporosis and fracture risk. A high vitamin A intake requires vitamin D to balance it. The epidemiological studies showing an association between high-normal vitamin A intake and reduced bone health all sported populations that were moderately to severely vitamin D deficient on average. At optimal vitamin D levels, 40-70 ng/mL 25(OH)D, it would take a whopping dose of vitamin A to induce toxicity. You might get there if you eat nothing but beef liver for a week or two.
The experiment hasn't been done under controlled conditions in humans, but if you believe the animal studies, the optimal intake for bone mineral density is a high intake of both vitamins A and D. And guess what? A high intake of vitamins A and D also increases the need for vitamin K2. That's because they work together. For example, vitamin D3 increases the secretion of matrix Gla protein and vitamin K2 activates it. Is it any surprise that the optimal proportions of A, D and K occur effortlessly in a lifestyle that includes outdoor activity and whole, natural animal foods? This is the blind spot of the researchers who have warned of vitamin A toxicity: uncontrolled reductionism. Vitamins do not act in a vacuum; they interact with one another. If your theory doesn't agree with empirical observations from healthy cultures, it's back to the drawing board.
High-vitamin cod liver oil is an excellent source of vitamins A and D because it contains a balanced amount of both. Unfortunately, many brands use processing methods that reduce the amount of one or more vitamins. See the Weston Price foundation's recommendations for the highest quality cod liver oils. They also happen to be the cheapest per dose. I order Green Pasture high-vitamin cod liver oil through Live Superfoods (it's cheaper than ordering directly).
So is vitamin A toxicity a concern? Not really; the concern is vitamin D deficiency.
Google Flu Trends
I just discovered a wonderful new tool from Google.org, Google Flu Trends. Google.org is the philanthropic branch of Google. Flu Trends gives you real-time data on flu incidence in your U.S. state, as well as for the country as a whole. Here's how it works:
I think this a fantastic use of the massive amount of raw information on the internet. It's amazing what a person can do with a brain and an internet connection these days.
We've found that certain search terms are good indicators of flu activity. Google Flu Trends uses aggregated Google search data to estimate flu activity in your state up to two weeks faster than traditional flu surveillance systems.Google's data match up well with U.S. Centers for Disease Control and Prevention (CDC) data on flu incidence, but are available 1-2 weeks before CDC data. Here's a comparison of Flu Trends and CDC data for previous years. Plus, Google makes the information easily accessible and user-friendly.
Each week, millions of users around the world search for online health information. As you might expect, there are more flu-related searches during flu season, more allergy-related searches during allergy season, and more sunburn-related searches during the summer.
I think this a fantastic use of the massive amount of raw information on the internet. It's amazing what a person can do with a brain and an internet connection these days.
Google Flu Trends
I just discovered a wonderful new tool from Google.org, Google Flu Trends. Google.org is the philanthropic branch of Google. Flu Trends gives you real-time data on flu incidence in your U.S. state, as well as for the country as a whole. Here's how it works:
I think this a fantastic use of the massive amount of raw information on the internet. It's amazing what a person can do with a brain and an internet connection these days.
We've found that certain search terms are good indicators of flu activity. Google Flu Trends uses aggregated Google search data to estimate flu activity in your state up to two weeks faster than traditional flu surveillance systems.Google's data match up well with U.S. Centers for Disease Control and Prevention (CDC) data on flu incidence, but are available 1-2 weeks before CDC data. Here's a comparison of Flu Trends and CDC data for previous years. Plus, Google makes the information easily accessible and user-friendly.
Each week, millions of users around the world search for online health information. As you might expect, there are more flu-related searches during flu season, more allergy-related searches during allergy season, and more sunburn-related searches during the summer.
I think this a fantastic use of the massive amount of raw information on the internet. It's amazing what a person can do with a brain and an internet connection these days.
Can Vitamin K2 Reverse Arterial Calcification?
It certainly can in rats. In April 2007, Dr. Cees Vermeer and his group published a paper on the effect of vitamin K on arterial calcification (the accumulation of calcium in the arteries). As I mentioned two posts ago, arterial calcification is tightly associated with the risk of heart attack and death. Warfarin-treated rats are an established model of arterial calcification. Warfarin also causes calcification in humans. The drug is a "blood thinner" that inhibits vitamin K recycling, and inhibits the conversion of vitamin K1 (phylloquinone) to K2 MK-4 (menaquinone-4). This latter property turns out to be the critical one in the calcification process.
Rats are able to convert vitamin K1 to K2 MK-4, whereas humans don't seem to convert well. Conversion efficiency varies between species. Dr. Vermeer's group treated rats with warfarin for 6 weeks, during which they developed extensive arterial calcification. They also received vitamin K1 to keep their blood clotting properly. At 6 weeks, the warfarin-treated rats were broken up into several groups:
In the group fed high K1 but no warfarin, there was about three times more K2 MK-4 in the aortas than K1, suggesting that they had converted it effectively and that vascular tissue selectively accumulates K2 MK-4. A high K1 intake was required for this effect, however, since the normal K1 diet did not reverse calcification. The rats fed high K2 MK-4 had only K2 MK-4 in their aortas, as expected.
What does this mean for us? K2 MK-4 appears to be the form of vitamin K that arteries prefer (although not enough is known about the longer menaquinones, such as MK-7, to rule out a possible effect). Humans don't seem to be very good at making the conversion from K1 to K2 MK-4 (at normal intakes; there are suggestions that at artificially large doses we can do it). That means we need to ensure an adequate K2 MK-4 intake to prevent or reverse arterial calcification; eating K1-rich greens won't cut it. It's worth noting that the amounts of K1 and K2 used in the paper were very large, far beyond what is obtainable through food. But the regression took only 6 weeks, so it's possible that a smaller amount of K2 MK-4 over a longer period could have the same effect in humans.
K2 MK-4 (and perhaps other menaquinones like MK-7) may turn out to be an effective treatment for arterial calcification and cardiovascular disease in general. It's extremely effective at preventing osteoporosis-related fractures in humans. That's a highly significant fact. Osteoporosis and arterial calcification often come hand-in-hand. Thus, they are not a result of insufficient or excessive calcium, but of a failure to use the available calcium effectively. In the warfarin-treated rats described above, the serum (blood) calcium concentration was the same in all groups. Osteoporosis and arterial calcification are two sides of the same coin, and the fact that one can be addressed with K2 MK-4 means that the other may be as well.
Both osteoporosis and arterial calcification may turn out to be symptoms of vitamin K2 deficiency, resulting from the modern fear of animal fats and organs, and the deterioration of traditional animal husbandry practices. So eat your pastured dairy, organs, fish roe and shellfish! And if you have arterial calcification, as judged by a heart scan, you may want to consider supplementing with additional K2 MK-4 (also called menaquinone-4 and menatetrenone).
The osteoporosis studies were done with 45 milligrams per day, which was well tolerated but seems excessive to me. Smaller doses were not tested. From the limited information available on the K2 content of foods, 1 milligram of K2 MK-4 per day seems like the upper limit of what you can get from food. That's about 40 times more than the average person eats. Anything more and you're outside your body's operating parameters. Make sure you're getting adequate vitamin D3 and A if you supplement with K2. Vitamin D3 in particular increases the secretion of MGP, so the two work in concert.
Rats are able to convert vitamin K1 to K2 MK-4, whereas humans don't seem to convert well. Conversion efficiency varies between species. Dr. Vermeer's group treated rats with warfarin for 6 weeks, during which they developed extensive arterial calcification. They also received vitamin K1 to keep their blood clotting properly. At 6 weeks, the warfarin-treated rats were broken up into several groups:
- One continued on the warfarin and K1 diet
- One was placed on a diet containing a normal amount of K1 (no warfarin)
- One was placed on a high K1 diet (no warfarin)
- The last was placed on a high K2 MK-4 diet (no warfarin)
In the group fed high K1 but no warfarin, there was about three times more K2 MK-4 in the aortas than K1, suggesting that they had converted it effectively and that vascular tissue selectively accumulates K2 MK-4. A high K1 intake was required for this effect, however, since the normal K1 diet did not reverse calcification. The rats fed high K2 MK-4 had only K2 MK-4 in their aortas, as expected.
What does this mean for us? K2 MK-4 appears to be the form of vitamin K that arteries prefer (although not enough is known about the longer menaquinones, such as MK-7, to rule out a possible effect). Humans don't seem to be very good at making the conversion from K1 to K2 MK-4 (at normal intakes; there are suggestions that at artificially large doses we can do it). That means we need to ensure an adequate K2 MK-4 intake to prevent or reverse arterial calcification; eating K1-rich greens won't cut it. It's worth noting that the amounts of K1 and K2 used in the paper were very large, far beyond what is obtainable through food. But the regression took only 6 weeks, so it's possible that a smaller amount of K2 MK-4 over a longer period could have the same effect in humans.
K2 MK-4 (and perhaps other menaquinones like MK-7) may turn out to be an effective treatment for arterial calcification and cardiovascular disease in general. It's extremely effective at preventing osteoporosis-related fractures in humans. That's a highly significant fact. Osteoporosis and arterial calcification often come hand-in-hand. Thus, they are not a result of insufficient or excessive calcium, but of a failure to use the available calcium effectively. In the warfarin-treated rats described above, the serum (blood) calcium concentration was the same in all groups. Osteoporosis and arterial calcification are two sides of the same coin, and the fact that one can be addressed with K2 MK-4 means that the other may be as well.
Both osteoporosis and arterial calcification may turn out to be symptoms of vitamin K2 deficiency, resulting from the modern fear of animal fats and organs, and the deterioration of traditional animal husbandry practices. So eat your pastured dairy, organs, fish roe and shellfish! And if you have arterial calcification, as judged by a heart scan, you may want to consider supplementing with additional K2 MK-4 (also called menaquinone-4 and menatetrenone).
The osteoporosis studies were done with 45 milligrams per day, which was well tolerated but seems excessive to me. Smaller doses were not tested. From the limited information available on the K2 content of foods, 1 milligram of K2 MK-4 per day seems like the upper limit of what you can get from food. That's about 40 times more than the average person eats. Anything more and you're outside your body's operating parameters. Make sure you're getting adequate vitamin D3 and A if you supplement with K2. Vitamin D3 in particular increases the secretion of MGP, so the two work in concert.
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