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Apr 23

Is redder, more oxygenated, skin judged as healthier, more desirable? Does the ability to detect a healthy cardiovascular system influence our choices of potential mates? Was our retinal system under evolutionary pressure to detect the oxygenation level of skin? Is the evolutionary importance of the signals presented by healthy oxygenated skin one of the foundations of the cosmetic industry?

Good skin blood flow and oxygenation is dependent on the underlying health of the cardiovascular, hormonal, and circulatory system. The detection of good blood flow in the skin is particularly noticeable in the face, and prominent in the cheeks. Hence, the general healthy look of rosy red cheeks we have all observed, and heard about. Evolution, being what it is, could it be that rosy red cheeks are used as a predictor in primates for a health, and hence a good mate choice?

Stephen et al., 2009 examined this exact issue. In their introduction the point out the various research that indicates the link between skin redness color and underlying ‘vascular’ health:

In humans too, skin redness caused by skin vasodilation and
vascularisation has connections to physiological status including
health. Additionally, blood oxygenation state is related to health
status and affects skin colour. In women, increased sex hormone levels
are associated with increased skin vascularisation [9] and vasodilatory
response [10], which arterializes the blood in the skin [11]. The
cutaneous vasodilator system becomes more responsive with physical
training [12], but is impaired in type 2 diabetes [13] and hypertension
[14]. Increased blood oxygenation is associated with increased
aerobic fitness [15] whereas increased blood deoxygenation is
associated with hypoxia and can lead to cyanosis (blue tinted skin),
which is indicative of coronary and respiratory illness [16].

Hence, it appears there is some validity to the idea of a healthy glow. Now in general the color red, not only in skin color but in any object, is associated with being vibrant and lively. But more particularly do humans pick up and judge people with redder skin as healthier, and more desirable?

The researchers hypothesis was that increased blood color in the face will be judged as healthier and oxygenated blood color would be considered healthier than deoxygenated blood color.

(side note: human oxygenated blood is 98-99% saturated with oxygen, deoxygenated blood is around 75% oxygen saturated)

First the scientist wanted to test if oxygenated skin blood color is judged as healthier than deoxygenated blood color. Subjects were presented with faces with varying degrees of oxygenated or deoxygenated color. These Caucasian faces (or later different ethnic faces), which were presented, had been transformed to match ‘redness’ of empirically collected data from oxygenated vs non-oxygenated faces. The subjects then were asked to alter the images (via photoshop like manipulation) along two axis - they could add ‘oxygenated’ color, or ‘deoxygenated’ color and their instructions were to ‘make the face as healthy as possible’.

The subjects were not told that these two manipulations were oxygenated and deoxygenated color.


The paler the faces the greater the increase in redness (both oxygenated and deoxygenated) was added by the subjects to make the faces look healthy. If the faces were already quite red (oxygenated) then less redness was added by the subjects. Hence, the faces which appear to have the least skin blood perfusion (pale) the greatest degree of redness was added to optimize the appearance of health.

While face pictures of both sexes were altered to increase redness,  more oxygenated color was added to female faces and more deoxygeneated color added to male faces (in comparison). The authors suggest that females faces are more ’sensitive’ to blood oxygenation color - but I am not sure what they really mean.

Overall, oxygenated blood color adding was judged as improving the look of healthiness compared to added deoxygenated blood color adding. This was consistent with the researchers hypothesis - but also makes sense in the general concept of a healthier look is judged by degree and amount of oxygenated blood is reaching the face (sign of a healthy cardiovascular system).

In an additional component of the study, the researchers found that participant ethnicity, or face ethnicity, did not result in any differences in the amount of color changes added by participants to optimize a healthy appearance. However, there was an interaction effect, with African participants adding more redness to African faces than the other faces. The authors did not offer much of an explanation for this finding.

The researchers conclude from their study:

The healthy appearance of faces is enhanced by increased blood
colouration in this study, suggesting that participants interpret skin
blood colouration as a cue to underlying health. This is consistent
with the established relationship between skin blood perfusion and
physiological status. Increased vasodilation and vascularisation of
the skin leads to increases in skin blood colour. These processes are
enhanced by increased levels of sex hormones in women [35], and
by physical training [36]. Skin blood flow is reduced in patients
with hypertension [37], type 2 diabetes [38], senescence [39] and
in smokers [40].

Beyond the idea that us humans use skin color to detect the underyling health of our fellow humans, the authors suggest their might be various levels of evolution going on:

Indeed, it has been suggested that the maximum sensitivities of the medium and long wavelength cones in the retinas of routinely trichromatic primates (a group which includes humans) are ideally suited for identifying small changes in blood perfusion and oxygenation in the skin of conspecifics [43]. The results of the current study suggest that the ability to perceive health cues provided by skin blood perfusion and oxygenation may be an additional advantage of trichromatic colour vision in primates.

(43: Changizi MA, Zhang Q, Shimojo S (2006) Bare skin, blood and the evolution of primate colour vision. Biol Lett 2: 217–221.)

This part seems like a stretch for me, that our retinas specifically evolved to detect healthy mates. Though I appreciate beauty as much as everybody else it seems to me there were many other important evolutionary pressures in retinal evolution (to find and catch prey, and avoid being prey as just a few important examples) other than to detect beautiful-health. But if further research indicates that skin color detection was so important that it fundamentally affected the evolution of our retinal system - well then praise beauty.

Out of curiosity I took a look at the abstract they cited (Changizi MA, Zhang Q, Shimojo S (2006)):

We investigate the hypothesis that colour vision in primates was selected for discriminating the
spectral modulations on the skin of conspecifics, presumably for the purpose of discriminating
emotional states, socio-sexual signals and threat displays. Here we show that, consistent with this hypothesis, there are two dimensions of skin spectral modulations, and trichromats but not
dichromats are sensitive to each. Furthermore, the M and L cone maximum sensitivities for routine trichromats are optimized for discriminating variations in blood oxygen saturation, one of the two blood-related dimensions determining skin reflectance. We also show that, consistent with the hypothesis, trichromat primates tend to be bare faced.

Okay, they have examined it at a reasonable level - though I am sure others in the field could come up with alternative points of discussion. I will be dig deeper - all in the name of evolution and beauty.

(strange thought: maybe you could see if individual differences in the ability to detect degrees of face coloration is related to specific ‘coloration’ gene polymorphisms. If true it would scare me a bit).

Stephen et al., give their summary paragraph at the end of the paper:

In the current study, we show that colour associated with skin blood
perfusion and oxygenation affects the healthy appearance of
human faces. Attractiveness, thought to signal underlying health
[60,61], and strongly related to perceived health [60] is a major
factor in human mate choice, particularly by men [62]. It is likely,
therefore, that the enhanced health appearance associated with
increased skin blood colour and oxygenation colour has consequences
for attractiveness and mate choice.

Take home message:

All of this really comes down to humans may use skin color/tone - rosy red cheeks - as a measurement of blood flow/oxygenation which is an indicator of general health. We would judge the rosy red cheeked faces as more desirable. Then this evolutionary desirability of health gets transformed in our higher language as beautiful / handsome, and a host of other similar words. But most biological signals are subject to manipulation. For how long have humans pinched their cheeks to bring about a rosy complexion? Moving onward to various natural substances that could be rubbed lightly on the cheeks. And from this a whole industry of ‘blush’ makeup was founded, and still flourish probably to the tune of multiple millions of dollars every year. Well instead of spending all that money on blush one could do things to increase your vascular health such as exercise. Instead of just signaling you are healthy, you could actually be healthy.

Is a healthy oxygenated skin color obtained via a healthy lifestyle not only a health hack but also a date hack :)

Apr 21
Film poster for An Inconvenient Truth
Image via Wikipedia

Thankfully the current generation of young people are far more aware of the environmental issues and willing to do something about it. They have taught their parents to recycle, use reusable grocery bags, to buy carbon credits (though controversial), etc, etc.  However, this same young generation is the fattest in our history (and potentially the least fit).

Does being overweight really coincide with the principles of trying to keep the planet healthy?

I have wanted to write a piece about this issue for awhile but didn’t have a nice published journal arguing what I thought were various obvious points, but now one has come out.

In a study published in the International Journal of Epidemiology by Edward and Roberts (2009) argues that food production is one of the main contributors (20%) to greenhouse gas emissions (H/T to esciencenews). If you have a population of people in the developed nations that are overweight (ranging from 20-65+ % of the population) this would have a number of implications. It costs more to transport the heavier people but also they are eating more than someone of normal weight and hence use up a greater amount of the valuable and dwindling energy resources and a greater amount of food producing land. This is not exactly rocket science to realize this.

Being overweight is equivalent to deciding to drive around in a SUV (or any other gas guzzler).

If people slimmed down (via escience news):

Transport-related emissions will also be lower because it takes less energy to transport slim people. The researchers estimate that a lean population of 1 billion people would emit 1.0 GT (1,000 million tonnes) less carbon dioxide equivalents per year compared with a fat one.

Really the comparison here was between a population of ‘lean’ with a mean body mass index (BMI) of 24.5 vs a more typical ‘developed’ country with a BMI of 29 (to give you a frame of reference normal weight is 18.5 -24.9, overweight is 25-29.9m and obese is 30+). The heavier population would consume 19% more food than the lean population.

I really don’t have to give you a bunch of numbers and facts I think all of you intuitively know that it only make sense that an overweight population consumes more energy and contributes a greater amount to environmental issues (including global warming).

I think the authors give a pretty clear statement in their discussion (GHG = global green house gases):

We argue that increased population adiposity, because of its contribution to climate change from additional food and transport GHG emissions, should be recognized as an environmental problem.

So if you care about the environment, be it you are young or old, then do your part and stay (or become) slim (meaning normal weight) - which will also contribute to your own health.

If you care about the planet’s health, then do something about it by taking care of your own health - by maintaining a healthy weight. Something for all of us to think about, but maybe this message has the best chance in taking hold in the current young generation who as a whole do care about the planet’s health.

Are you a gaz guzzler, a hybrid, an all electric, or even a highly efficient bicycle?

Mar 16
Silhouettes representing healthy, overweight, ...
Image via Wikipedia

What is your body mass index (BMI) - you can check it here or here (metric): normal weight = 18.5 - 24.9, overweight = 25.0 - 29.9, obese = 30.0 +)

Do you want a properly working brain - then don’t become overweight (now you don’t have to read the rest of the piece). You are your brain, or at least it is the one thing you can not afford to lose. New research indicates that being overweight is related to reduced cognitive ability.

While some recent papers I have been reading indicates to me that being overweight (BMI 25-29.9) or even obese (BMI 30+) does not cost you that much in terms of earlier death (Fontaine et al., 2003, Pischon et al., 2008) (I will try to cover this more fully in another post) however, you may forfeit a fully functional mind.

High BMI related with lower prefrontal cortex activity and worse mental ability in healthy subjects:

Volkow et al., 2009 studied 21 healthy subjects who had BMIs in the range of 19-37, with 3 subjects in the obese range (BMI 30+). The researchers found that a significant negative correlation (relationship) between BMI and reduced activity (as measured by metabolism) in the prefrontal cortex, when the brain was at rest (baseline). What this means is the higher your BMI the less active the prefrontal cortex is. The prefrontal cortex is the part of your brain responsible for controlling higher cognitive function (planning - thinking).

But more interesting is that the baseline metabolic activity level associated positively with a number of mental performance measurements (memory as measured by the California Verbal Learning task, and executive function via the Stroop interference task, and Symbol Digital Modality test).  Therefore, the subjects with a high baseline prefrontal cortex metabolism (smaller BMI) performed the best on these mental tasks. At the opposite end of the spectrum, the high BMI individuals with low prefrontal baseline activity performed the worse on excutive function and memory tests.

Interestingly, during the cognitive tasks there was no correlation between prefrontal brain metabolism and BMI or performance on the mental tasks.

Healthy overweight individuals have lower ‘thinking’ ability: more papers finding the same trend (with larger number of subjects):

While one of the short comings of the above paper is the small number of subjects, several other papers with large number of HEALTHY subjects have found similar trends of high BMI related with reduced cognitive ability (Sabia et al., 2009 n = 5,131, Gunstad et al., 2007 n= 408). Interestingly, Sabia et al., 2009 not only found overweight individuals (BMI 25+) but also underweight people (18.5 or less) had reduced cognitive ability in late middle age compared to ‘normal’ weighted individuals.

The consistent finding among these three studies is the executive function is reduced as the BMI increases, even in otherwise healthy individuals. Executive function (thought to mainly be controlled by the prefrontal cortex) measures your general cognitive ability - planning, cognitive flexibility, abstract thinking, initiating appropriate actions and inhibiting inappropriate actions - or you could executive function just call this plain old thinking. This reduced executive ability in the overweight individual could play into my theory of American’s weight gain could be tied into the rise of debt (I will follow up on this theme in the future).

Increase BMI related to reduced gray matter in the brain:

Adding to the overall gloomy picture is a study of 1,428 healthy individuals in which the researchers found high BMI correlated with reduced brain gray matter in men (Taki et al., 2008). They found no relationship between BMI and gray matter in women, and go onto to speculate the higher levels of visceral fat in men (compared to women with similar BMI) could be the mediator of the reduced gray matter in high BMI men.

Take home message:

If you want to keep your brain’s gray matter (if you are a man), and your ability to plan and think at your best level then don’t become overweight (men and women). The general finding is not just for obese people (BMI 30+) but also for overweight people (BMI 25 - 29.9). Also being underweight (less than 18.5) is related to reduced cognitive ability. And all of these results are based on otherwise healthy individuals.

What is your BMI? go check it out here or here (metric).

You might not lose too many years of life due to being overweight (because of medical advances keeping your heart pumping) but you won’t be playing with a full deck upstairs - ouch!

Feb 25

Would you believe me if I told you only 11% of patients are receiving rigorous scientifically backed evidence based treatment (at least in the case presented below)?

For argument sake let us presuppose that your overall health is half based on you doing the correct things (making healthy lifestyle choices), and half based on your doctor doing the right thing.

It is an open argument if most of us in the developed world who have the opportunity to make the correct lifestyle choices actually choose wisely - but again for argument sake and based on most of the readers of this blog are probably mostly making the wise healthy choices what about the other half of the equation - the doctor choices of the appropriate treatment for you?

According to a recent study (Tricioci et. al., 2009, published in the well respected JAMA journal) reported in the Wall Street Journal regarding heart disease treatment the numbers do not look good. Of the 2,700 heart disease patients only 11% of the patients received treatment supported by high-quality scientific evidence. About 50% of the treatments given had limited scientific backing. From the WSJ article:

The findings from the JAMA study reflect the challenge doctors and patients face in choosing the best course of treatment for a variety of conditions. And they underscore that even though drug and device companies, government agencies and philanthropic groups have spent billions of dollars developing and testing new treatments in recent years, much of what happens in the doctor’s office or the hospital operating suite might not be based on rigorous scientific evidence.

To give you a bit of background of what is, or is not, considered good scientific evidence I quote from the WSJ article.

The American College of Cardiology and the American Heart Association have been jointly issuing guidelines to doctors on care of cardiovascular patients for more than 20 years. Recommendations based on multiple randomized clinical trials, in which patients are randomly assigned a treatment, are considered having the highest level of evidence. A single randomized study or non-randomized studies comprise the second level, while recommendations backed by expert opinion or case studies are considered having the weakest evidence. Guidelines are also ranked by whether empirical evidence or general opinion supports that a treatment is useful and effective or not.

Now I believe it isn’t the case that the doctor is necessarily doing anything wrong - the problem is the lack of adequate clinical trials testing which treatment is actually most effective compared to weaker evidence including such things as ‘expert opinion’. Opinion based on experience is valuable, but it is not science - though sadly in many cases it is the best we have.

However, things may change in the future with the new Obama administration as reported in WSJ.

This month, the Obama administration and Congress budgeted more than $1 billion of the economic stimulus package to fund research for comparing the effectiveness of different treatments in head-to-head studies aimed at providing evidence to clinicians and insurers on the best treatment strategies.

“We need those studies to make the kind of changes in health care that are being talked about — being sure we get the best possible care for our patients in the most cost-effective manner,” says Sidney Smith, a medical guidelines expert and cardiologist at University of North Carolina, Chapel Hill and senior author of the JAMA paper.

Though with the current state of the economy I wonder if this will be possible - I hope so. In most cases the the drive behind most large clinical trials are pharmaceuticals trying to get a new drug approved. From the WSJ article:

One reason for the lack of stronger evidence is that the large “megatrials” that have dominated cardiovascular research in the past decade were sponsored by drug and device companies. While those studies provide an important source of information, they are typically designed primarily to win approval for a treatment or to widen the market for a therapy already on the market, and not to guide treatment decisions, according to the JAMA study.

I am not sure what to say - it appears many times the clinical studies have not been performed and we simply do not know what is the most effective treatment for various health conditions (I will try to ignore the most ‘cost effective’ treatment discussion). Clinical trials are expensive and there are many variables you have to worry about (e.g. individual patients additional complications) and so as a society we might not be able to afford to thoroughly test what is the most effective treatment out of all the options that currently exist. One thing the above research suggest is for the patient do their best to be informed and knowledgeable (though this is not an easy task).

The second thing the above research brings to mind is you might want to pay even more attention to the half of the health equation you have more control over - you making the best daily health choices.

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