Surprisingly, though, it does not increase longevity in
normal, healthy mice when started in middle age
By Will Block
een any hobgoblins lately? They cause no end of mischief because, well, that’s what they’re meant to do. Without hobgoblins, life would be too darned easy . . . and dull. Our minds would not be boggled by things that confound us, like some of what’s reported in this article. (“Boggle,” by the way, comes from the Scottish word “bogle,” which means hobgoblin or bogey, as in bogeyman.) This article is about a hobgoblin of sorts.
When something sounds too good to be true, it usually is too good to be true. Be wary, and look for the catch. Just because there is one, however, doesn’t necessarily mean that the something in question isn’t still good—it may merely mean that it’s not as good as had been genuinely believed by honest people.
Such a situation now presents itself with regard to resveratrol, which seems to have acquired its very own hobgoblin for the purpose of messing with our minds. Here’s the situation: until now, virtually everything we knew about resveratrol (pronounced rez·VEER·ah·troll), the fabled red-wine compound that has set the biomedical world on fire, led to two broad conclusions:
(1) resveratrol strongly protects against degenerative diseases of aging, such as cardiovascular disease, cancer, arthritis, and neurodegenerative diseases; and (2) resveratrol dramatically extends average and maximum lifespan in every organism in which it’s been tested, namely, certain species of yeast, roundworms, fruit flies, fish, and—most importantly because they’re mammals, and thus closely related to us—mice.
Either of those conclusions would be enough to catapult any chemical compound to scientific stardom, with the prospect of a Nobel Prize in medicine or physiology dangling before those who pioneered the research in question. Together, the two conclusions are so spectacular that they sound, well, too good to be true. Both of them, nonetheless, are still firmly believed to be true, based on solid scientific evidence. But . . .
An Inconsistency Rears Its Ugly Head
Enter the Resveratrol Hobgoblin (looking remarkably like a bunch of rotten grapes). The little bugger has caused the results of a recent study of resveratrol in mice to be inconsistent with the longevity conclusion, i.e., inconsistent with almost all the prior research leading to it.* And the study is highly credible, so it cannot be swept under the rug. We must confront it and try to understand the somewhat altered picture of resveratrol it has painted.
The study was conducted by an international team of investigators under the leadership of two top-ranking experts in the field: Rafael de Cabo of the National Institute on Aging, National Institutes of Health (USA), and David Sinclair, director of the Paul F. Glenn Laboratories for the Biological Mechanisms of Aging, Harvard Medical School. (If you’ve been reading our articles on resveratrol over the last several years, Dr. Sinclair’s name will be familiar to you.)
Resveratrol Increased Longevity in Obese Mice . . .
The same two researchers and their respective teams of colleagues had published a groundbreaking study in 2006 in which they reported that dietary supplementation with resveratrol strongly protected obese mice on a high-calorie diet from major degenerative diseases of aging, including diabetes (even though it did not reduce their weight). Furthermore, it increased their maximum lifespan by about 15–20%! It was as though the obesity had no effect on their health or longevity—an astounding discovery.
The researchers had used obese mice because their primary interest at the time was in the potential therapeutic benefits of resveratrol against type 2 diabetes, for which the primary risk factor is obesity. Their results, it can be assumed, exceeded their wildest expectations, and the study garnered a great deal of publicity in the press, both scientific and popular. But an important question remained: What about normal, healthy (nonobese) mice? Would they benefit similarly from resveratrol?
. . . But Not in Normal Mice
We now have the answer: yes and no. Yes to the long-term health benefits, but no to the longevity benefit. The latter result was surprising and disappointing. Before getting to that, let’s see how the new study was conducted. The subjects were normal, healthy, 1-year-old mice (roughly equivalent to 35 years of age in humans). They were divided into three groups based on diet: (1) a nutritious standard diet (SD) of mouse chow; (2) every-other-day (EOD) feeding of a nutritious diet; and (3) an unhealthy, high-calorie (HC) diet, with 60% of the calories coming from fat. Each of these groups was further divided into resveratrol supplementation (at two different doses) or no resveratrol (the controls). Thus there were nine groups altogether. (Actually, there were more than that, but we’ll get to that later.)
EOD feeding, in which the mice can eat as much as they want every other day, but nothing in between, is a mild but still somewhat effective variant of caloric
restriction (CR). The latter is a severe but nutritionally adequate, well-balanced daily diet containing about 30–40% (sometimes up to 50%) fewer calories than would be consumed in a normal diet. In experimental organisms of many species, CR is the healthiest dietary regimen known: it protects strongly against degenerative diseases of aging, and it dramatically extends both average and maximum lifespan.*
Dietary Restriction—Unanswered Questions
Sound familiar? The reason why these benefits are also attributed to resveratrol is that resveratrol appears to stimulate the same metabolic pathways that are the basis for CR’s antiaging effects. There is strong scientific evidence to support this thesis, but that does not mean that the two mechanisms in question are entirely the same. In fact, they are not entirely the same, as other evidence has shown, and the situation is rife with complexity and confusion. There are many unanswered questions regarding the several mechanisms, in addition to CR mimicry, by which resveratrol improves health and longevity.
It’s also worth noting that, although EOD feeding and CR have similar effects on health and longevity, the physiological mechanisms involved have not been shown to be the same—which is not the same as saying that they have been shown to be different. The question is unanswered, but it’s likely that there are both similarities and differences. In any case, both EOD and CR can be described by the more general (but vague) term dietary restriction (DR), which says nothing about schedules or calories.
Why the Number 0.081 Is Important
Now let’s get back to the healthy mice and see how they reacted to the resveratrol. Most of the experiments were conducted using two dosages, defined as 100 and 400 mg of resveratrol per kg of food consumed. For our purposes, that’s an inconvenient way to define them. Based on the average body weight (35 g) of the mice and the amount of food they ate (about 2.5 g per day), the two dosages translate to an average of about 7 and 28 mg of resveratrol per kg of body weight per day, respectively. These amounts are not much greater than those used in the researchers’ earlier study (5.2 and 22.4 mg/kg per day), in which the higher dose was found to be more effective (the same turned out to be true in the new study as well).
To convert the dosages in the new study to human equivalents, we multiply by the standard mouse-to-human scaling factor, 0.081, which reflects the major differences between body surface area and metabolic rate between the two species. This gives 0.57 and 2.3 mg/kg per day, respectively, so for a 75-kg (165-lb) person, those numbers become daily doses of 43 and 173 mg, respectively. Since red wine contains about 1 mg of resveratrol per bottle, on average, it would take about 43 or 173 bottles per day to provide these amounts. (Cheers!) They can easily be obtained, however, through supplementation.
Resveratrol Enhances Cellular Energy
Production and Survival
With their mice at the relatively advanced age of 27 months, the researchers found, first of all, that the regimen consisting of the standard diet with the higher dose of resveratrol (let’s call it SD+R) strongly mimicked the physiological effects of EOD feeding (without resveratrol) in terms of patterns of gene expression, i.e., in terms of the relative levels of activity of numerous genes involved in these effects. This was determined by analysis of four types of tissue: liver, skeletal muscle, adipose (fat), and heart.
Among the notable effects observed with SD+R were: (1) an increase in mitochondrial gene expression in liver and heart cells (mitochondria are the cellular “power plants” where the chemical energy for life processes is generated); and (2) a decrease, in all four types of tissue, in apoptosis, the natural process by which cells die off. Together, this means that cells became more efficient at energy production, and they lived longer.
The average increases in lifespan were
by 26% and 25% for the lower and
higher resveratrol doses, respectively.
And the lower dose significantly
increased the maximum lifespan.
The similarity between the effects of resveratrol and EOD feeding on gene-expression patterns in various tissues was mirrored, in another recently published study, by the similarity between the effects of resveratrol and CR. In that study, interestingly, the resveratrol dose used was fairly low, with a human equivalent of only 30 mg per day. (See
“Low-Dose Resveratrol Prevents Cardiac Aging” in the August 2008 issue.)
How About a Younger Liver?
The researchers sought to determine which of the two regimens—SD+R or EOD—had the greater effect on tissue aging in the elderly mice (27 months). They found that, in liver tissue, both treatments produced gene-expression patterns similar to those of mice that were
9 months younger, while only resveratrol had this effect in skeletal muscle tissue. In adipose tissue, by contrast, both treatments increased the effects of aging, and in heart tissue they had no significant effect. Thus the results of these treatments were strangely mixed.
In the researchers’ earlier study, they showed that, in the liver, the higher dose of resveratrol opposed most of the transcriptional changes (changes in gene expression) induced by a high-calorie (HC) diet. Using more refined techniques in the new study, they confirmed this gratifying result and extended it by showing that the same was also true for the other three types of tissue studied: skeletal muscle, adipose, and heart. These results support the conclusion that resveratrol treatment induces transcriptional changes resembling those of mice on a lower-calorie diet.
Unfortunately, the researchers were unable to shed any new light, in this study, on the role of a particular protein, SIRT1 (encoded by a gene called SIRT1), that is believed to play a central role in the antiaging mechanisms of both caloric restriction and resveratrol (and, perhaps, EOD feeding). For more on this subject, see the sidebar.
Exploring How Resveratrol Works
Resveratrol does not work its magic by magic—there must be a biochemical mechanism (or two, or three, or . . .). A great deal of evidence suggests that the primary mechanism involves resveratrol’s activation of a protein called SIRT1, whose central role in the physiology of caloric restriction (CR)—and, apparently, of resveratrol—has made it the object of intense scientific interest. SIRT1 is the most important member of a family of proteins called sirtuins (sir·TOO·ins), of which there are seven in mammals.
It would be interesting to know what happens when the activation of SIRT1 is brought about not by CR or by resveratrol, but by itself. That sounds impossible, like pulling oneself up by one’s bootstraps. But scientists have many tricks up their sleeve, and one of them is gene splicing, a technique for inserting genes into the DNA of an organism. They can, for example, make a copy of the SIRT1 gene from a mouse and splice it into the mouse’s DNA so that the latter contains two such genes (the offspring will have two also). This will tend to double (or more than double, depending on various factors) the production of the SIRT1 protein in the animals’ tissues.
One type of gene splicing
This technique is useful for identifying physiological effects that are due to SIRT1 alone. Such a “clean” analysis is not possible with CR or resveratrol, because they also affect the production of the other six sirtuins (in ways that are poorly understood). Furthermore, they induce other, non-sirtuin-dependent biochemical pathways whose effects may overlap with those of SIRT1, making it very difficult to sort things out.
Mice that have been genetically engineered as described above are called transgenic mice. A group of researchers in the United States and Spain recently published a study in which such mice were tested to determine the role of SIRT1 in certain aspects of energy metabolism. In various tissues of the transgenic mice, the level of activity of SIRT1 was anywhere from 2 to 4 times greater than that in the normal control mice.
The researchers found, first of all, that excess SIRT1 activity had no effect on body weight in mice on a standard diet (SD). With a high-calorie (HC) diet, the mice became obese, but there were no statistically significant differences in body weight, fat mass, or lean mass between the transgenic HC mice and the control HC mice. There was, however, something quite intriguing: the transgenic mice ate considerably more than the controls, yet they didn’t gain more weight than the controls (in fact, they tended to gain a little less).
This could mean only one thing (and the researchers’ experiments confirmed it): the excess caloric intake in the transgenic mice must be compensated for by an increase in energy expenditure. Thus, excess activation of SIRT1 exerts a positive influence on energy metabolism, a conclusion that jibes with the results of studies using resveratrol.*
This conclusion has significant implications with regard to a potential protective effect against insulin resistance and its awful spawn, type 2 diabetes. On a broader scale, it implies protection against the metabolic syndrome, a group of five deleterious conditions that collectively pose a strong risk for diabetes, cardiovascular disease, neurodegenerative diseases, and more. These five conditions are visceral obesity, insulin resistance, high triglycerides, low HDL-cholesterol (the “good cholesterol”), and hypertension.
The chief culprit here is an excessively fatty (HC) diet, which triggers a witches’ brew of metabolic disorders, especially in the liver. Notorious among them is nonalcoholic fatty liver disease (NAFLD), which is characterized by the accumulation of fatty deposits in the liver, with myriad harmful consequences. In the transgenic HC mice, this condition was almost entirely prevented by the action of SIRT1. Also substantially prevented was fat-induced glucose intolerance.
The researchers believe these effects may have been brought about in part by the observed protective effect of SIRT1 against inflammatory processes in the liver, together with upregulation of certain antioxidant enzymes. The anti-inflammatory action (which is seen with resveratrol treatment) is probably linked with anticancer and antiaging mechanisms.
- Pfluger PT, Herranz D, Velasco-Miguel S, Serrano M, Tschöp MH. Sirt1 protects against high-fat diet-induced metabolic damage. Proc Natl Acad Sci USA 2008;105(28):9793-8.
Resveratrol had no effect, by the way, on body weight in the SD or EOD mice. In the HC mice, the lower dose of resveratrol increased body weight significantly, while the higher dose tended to reduce it. The reasons for this are unclear.
Resveratrol Delays Functional Decline
In other experiments, the researchers found a variety of evidence for the beneficial role of resveratrol in preventing disease and retarding the aging process. In the elderly mice on the standard diet, there were marked reductions in signs of aging (compared with the controls), including:
- Improved structure and strength of bones, indicating better bone health (which, in humans, would mean a reduced risk for osteoporosis). This was true for both the lower and higher doses of resveratrol.
- A significantly reduced incidence (with the higher dose of resveratrol) of cataracts at 30 months of age versus 18 months, when there was not yet any difference.
In the elderly mice on the high-calorie diet, resveratrol at both the lower and higher doses reduced the severity of albuminuria, the presence of abnormal amounts of protein (chiefly albumin) in the urine. This condition, which is linked with obesity, is usually indicative of disease, especially vascular or kidney dysfunction, and is a risk factor for cardiovascular disease.
- Improved locomotor function, i.e., improved balance and coordination, with the higher dose of resveratrol. This means a reduced risk of falling, an obvious advantage in the elderly.
Resveratrol Improves Cardiovascular Function
For their studies of the effects of resveratrol on cardiovascular function, the researchers used a third dosage that was 6 times higher than the “higher” dose discussed above, namely, 2400 mg of resveratrol per kg of food consumed. The human equivalent, for a 75-kg person, is about 1038 mg per day (1038 bottles of wine!). This “HR” dose was given to mice on both the standard diet and the high-calorie diet, which we can abbreviate as SD+HR and HC+HR, respectively.
The researchers observed the following cardiovascular benefits:
- A significant reduction in total cholesterol levels after 10 months of treatment (SD+HR), with a trend toward lower values of triglycerides (fats). Oddly, cholesterol was not tested in the HC+HR mice.
- Increased elasticity of the aorta—an important indicator of good vascular health. Age-related aortic dysfunction (stiffening of the vessel walls) was not only prevented by resveratrol (SD+HR), it was actually improved beyond that of age-matched SD controls to the level of 3-month-old mice. In obese mice, resveratrol (HC+HR) protected against aortic dysfunction such that there was no difference between them and age-matched SD controls.
- Strong protection against oxidative stress caused by free radicals, as measured in the aorta. With SD+HR, oxidative stress was reduced to the levels of 3-month-old mice, and with HC+HR, it was reduced to the levels of age-matched SD controls.
- Increased capacity, with both dietary regimens, for the production of nitric oxide (NO), the signaling molecule that plays a central role in facilitating vasodilation, which lowers blood pressure.
- Decreased apoptosis in the vascular endothelium (the layer of smooth, flat cells that line the blood vessels). Apoptosis increases with aging and is further increased by obesity. In the SD+HR and HC+HR mice, these increases were eliminated.
Resveratrol Increases Longevity—
Except When It Doesn’t
- Decreased inflammation in the vascular endothelium. In measurements of five different markers of inflammation, resveratrol attenuated the effect in all five cases with SD+HR and in two cases with HC+HR.
Now we return to the matter of longevity, which has become hobgoblin territory. The results seen in this study were surprising and disappointing. With the two resveratrol doses that were used in most of the work described above (i.e., not the dose used in the cardiovascular experiments), there was no longevity effect in the SD mice: the mortality rates with resveratrol were the same as in the controls.
On the other hand, the new study confirmed the results of the earlier study, which used only obese mice. In the new study, the HC control mice (no resveratrol) had a substantially lower survival rate than the SD controls (normal, healthy mice), because obesity shortens lifespan. And with both of the resveratrol doses, the survival rates of the HC mice matched those of the SD controls! In other words, the HC survival rates with resveratrol substantially exceeded those of the HC controls, meaning that resveratrol increased longevity in the obese mice, as it had in the earlier study.
The average increases in lifespan were by 26% and 25% for the lower and higher resveratrol doses, respectively. The lower dose, furthermore, significantly increased the maximum lifespan of the mice (despite its having increased their body weight, as noted above), whereas the higher dose (which tended to decrease body weight) did so to a lesser, and not statistically significant, degree. Thus the longevity effects were not related to body weight.
With the EOD mice on resveratrol, things were not much different than with the SD mice. Although all three groups (two resveratrol doses and the EOD controls) lived about 15% longer than the SD controls (because even this kind of dietary restriction promotes longevity), this effect was statistically significant only with the lower of the two resveratrol doses. And among the three groups themselves, there were no significant differences.
The researchers had one more test to perform: they looked at the effect of the very high dose of resveratrol (from the cardiovascular experiments) on longevity in the SD mice. There was no effect—another disappointment. (Oddly, they did not do this test on the HC mice.)
Resveratrol Reduces Oxidative Stress and Inflammation
It’s all very confusing, isn’t it? Despite resveratrol’s beneficial effects in preventing an astonishing array of seemingly unrelated diseases and disorders associated with aging, it appears not to increase longevity in normal, healthy mice. The researchers speculated that this might be due to the relatively late onset (at 1 year, or early middle age) of its initiation. In that sense, it’s analogous to the manner in which dietary restrictions such as EOD and CR become less effective as the age at which they’re initiated increases. The next step is to investigate the effects of initiating resveratrol treatment in healthy mice at weaning—and that study is underway.*
“. . . we show that resveratrol improves
cardiovascular function, bone density,
and motor coordination, and delays
cataracts, even in nonobese rodents.”
The researchers pointed out that many of the effects observed with resveratrol involved a generalized reduction in oxidative stress and inflammation. This is consistent with the known health- and longevity-promoting effects of DR, which are believed to be strongly related to reductions in these two factors. It’s also gratifying to know that postmortem examination of the mice showed no evidence of any kind of tissue damage or other abnormalities associated with the use of resveratrol. The authors mentioned, however, that extremely large doses of resveratrol (many times greater than the largest dose they used) are known to be harmful to rodents.
The authors stated,
In conclusion, long-term resveratrol treatment of mice can mimic transcriptional changes induced by dietary restriction and allow them to live healthier, more vigorous lives. In addition to improving insulin sensitivity and increasing survival in HC mice, we show that resveratrol improves cardiovascular function, bone density, and motor coordination, and delays cataracts, even in nonobese rodents. . . . Since cardiovascular disease is a major cause of age-related morbidity and mortality in humans but not mice, it is possible that DR mimetics such as resveratrol could have a greater impact on humans. However, resveratrol does not seem to mimic all of the salutary effects of DR, in that its introduction into the diet of normal 1-year-old mice did not increase longevity.
don’t You just Hate inconsistency?
It’s human nature that we generally want things to be consistent, and when they’re not, it’s unsettling.* With resveratrol, the picture has, until now, been so consistently favorable—indeed, phenomenal—that it’s all the more disconcerting to find a fly in the ointment.
Some of the wind has indeed been taken out of resveratrol’s splendid sail. But let’s keep things in perspective, shall we? Resveratrol is still, by any measure, the Holy Grail of antiaging, with a list of accomplishments that nothing else in the world of medicine can match. That’s not bad for a little ol’ molecule found in grapes.
- Pearson KJ, Baur JA, Lewis KN, Peshkin L, Price NL, Labinskyy N, Swindell WR, Kamara D, Minor RK, Perez E, Jamieson HA, Zhang Y,
Dunn SR, Sharma K, Pleshko N, Woollett LA, Csiszar A, Ikeno Y, Le Couteur D, Elliott PJ, Becker KG, Navas P, Ingram DK, Wolf NS, Ungvari Z, Sinclair DA, de Cabo R. Resveratrol delays age-related deterioration and mimics transcriptional aspects of dietary restriction without extending lifespan. Cell Metabol 2008 Jul 2 [online preprint].
- Bass TM, Weinkove D, Houthoofd K, Gems D, Partridge L. Effects of resveratrol on lifespan in Drosophila melanogaster and Caenorhabditis
elegans. Mech Ageing Dev 2007;128:546-52.
- Baur JA, Pearson KJ, Price NL, Jamieson HA, Lerin C, Kalra A, Prabhu VV, Allard JS, Lopez-Lluch G, Lewis K, Pistell PJ, Poosala S, Becker KG, Boss O, Gwinn D, Wang M, Ramaswamy S, Fishbein KW, Spencer RG, Lakatta EG, Le Couteur D, Shaw RJ, Navas P, Puigserver P, Ingram DK, de Cabo R, Sinclair DA. Resveratrol improves health and survival of mice on a high-calorie diet. Nature 2006 Nov 16;444(7117):337-42.
Will Block is the publisher and editorial director of Life Enhancement magazine.