Why are people susceptible to so much disease?
How is it that the most sophisticated creatures on planet earth succumb, sometimes completely, to some of the most simplistic viruses, like the flu? We would expect that our bodies have seen every intruder possible in our evolutionary trek to becoming human – and should have developed a solution. But we haven’t.
In fact, diseases continually beat our best efforts to coral them. Just today the New York Times ran a story about the resurgence of a virulent form of malaria that appears resistant to even the newest drugs designed to defeat it. Back in 2003, the SARS epidemic swept around the world – into 37 countries, claiming 1,000 lives – in only a matter of weeks. Lest we forget bird flu and the continual fear that we may repeat the 1918 flu pandemic.
All of these examples serve as a reminder that human beings are no closer to having tamed mother nature than we were 50,000 years ago. So, what then is this evolutionary step that has made us so susceptible to microscopic pathogens? A fascinating physician-scientist may have uncovered the answer.
A Man on a Different Mission
San Diego, California is not what comes to mind when you think ‘medical research‘. Over at the University of California San Diego, however, a group of researchers led by Dr. Ajit Varki are proving real, meaningful work can be done while it remains a constant, sunny 75 degrees outside.
Dr. Varki took a different path to get to where he is today, atop the research world – commanding his Glycobiology Research and Training Center at UCSD. He wasn’t thinking about the bird flu, AIDS or any other disease when he started out really. Instead, Varki was curious about the surface of cells from his initial studies of blood. In particular, he was perplexed by the complexity of the sugar molecules that make up the outside of a cell. He noted that:
“The cells in the body are not like the planet Mars; it’s like the planet Earth – it has all this stuff on it.”
Continuing with his planetary analogy, Varki first turned his energy towards the “tips of the trees” peaking off these planetary cells, called sialic acids. He observed that when some bone marrow cancer sufferers were administered with a horse serum to help restore their bone marrow, they inevitably developed an adverse reaction – not too dissimilar from the way human’s will reject someone else’s organ transplants.
Varki and other scientists took this lead and discovered that humans differed from every other species – even our genetic cousins, the great apes – in that we lack the gene to convert some of our sialic acid sugars into the form common in all other animals. In effect, human beings are an evolutionary outlier – a “sialic quirk” in the words of Varki.
The Difficult Life of an Outlier
Varki wanted to investigate this lead further, so he took off to The Yerkes National Primate Research Center in Atlanta to confirm some of his findings against our nearest genetic cousins, the Chimpanzee. He compared known health statistics between the chimp and humans with some startling results.
Despite the fact our genetic code is 99% identical to that of a chimps, human populations tend to suffer from cancer at a rate over 20% while, in chimps, that rate is only 2-4%. And even though humans initially contracted HIV from chimps, when HIV is injected back into chimps, they are incapable of developing full-blown AIDS. Chimpanzees do not suffer from any of malaria’s effects. They don’t even have the same kind of heart attacks as humans, suffer from zero rheumatoid arthritis, etc. The list goes on.
The take home message from Varki’s research is a profound one: most of the diseases we loathe are only able to attack humans by acting like our sialic acids. This process – known in the medical world as molecular mimicry – is a brutal battle waged between the sialic acids and diseases like the flu. Varki has likened this battle to “500 million years of an evolutionary arms race.” One side may gain a lead, but the other will inevitably return.
Varki and his team have narrowed the time in which this evolutionary development occurred to the very recent period when humans evolved from the great apes, meaning sialic acids could prove to be key in understanding the evolution therein.
Watch Professor Varki Explain His Work, 55 Minutes (and worth every minute of your time):
Making the Sialic Acid Diet Connection
Evolutionary speculation surrounding this work can reach a fever pitch but there are some practical findings related to nutrition that have come out of this work. Very recently, Varki and his team published some interesting findings relating to how the human body reacts when it comes in contact with these foreign sialic acids.
While these intruder sialic acids may seem foreign, they, in fact, come from a source we know all too well – meat. Varki, et al. found that each human, on average, takes in 25-150mg of this foreign, animal sialic acid a day [source: http://www.youtube.com/watch?v=Vd9BZajbWY0 minute 29:02 ], through the consumption of animal meat and milk products – and most of it accumulates in our blood vessels.
Interestingly though, humans also have massive quantities of meat sugar antibodies circulating in our bloodstream. These antibodies are created, at least in part, because the body recognizes it must deal with foreign sialic acids on a regular basis. It was then that Varki noticed something strange – cancerous tumors contain high amounts of this foreign sialic acid. That created a red meat paradox of sorts:
How is it that these antibodies allow cancerous tumors, ripe with the very sialic acids these antibodies were created to defend against, to exist in the body?
The sialic team set out to solve this puzzle by injecting special mice breed to resemble humans with sialic acid antibodies while keeping half of the mice free of antibodies as a control. The researchers found that the antibodies created a low grade inflammation with the red meat sialic acids in the treated mice – and that inflammation is causing tumors to grow larger than they would otherwise.
Where We Go From Here
This research helps explain earlier findings – some from as far back as the 1970s – that showed red meat increases your cancer risk. Varki himself claims he has observed that cancer is more prevalent in those who consume more red meat in unpublished work during the video above. These opinions fall in line with voluminous amounts of research, including the opinion of the American Cancer Society, showing that eating less meat and more vegetables decreases cancer risk.
What Varki, et al. have really done here is give some teeth to the idea of why red meat increases your cancer risk. It appears that the inflammatory response from sialic acids and their antibodies creates a good environment for cancer – and we are better for having this nugget of knowledge.
However, jumping from here to a blanket statement recommending a ban on meat – or even drastically reducing it – may be premature.
These findings deal with genetically altered mice that demonstrate the sialic acid-related inflammation but how that may apply to humans is a bit more difficult to predict in our opinion. We know there is a dramatic difference in the nutritional makeup of meat depending upon how it was raised. Research has shown a remarkably improved nutritional profile in pastured raised cows that eat grass and free range chickens that poke around in the yard; both these chickens and cows had dramatically higher amounts of Omega 3 and Vitamin E when raised properly.
It may just turn out that sialic acid content in all forms of meat – factory farmed with GMO corn feed or pastured raised on grass – turns out to be roughly the same. Or, knowing the dramatic effects proper diet had on the nutritional composition of their meats, it may be that sialic acid content is reduced dependent upon the type of feed they eat, the way they are raised, etc.
All of this is obviously wild speculation but the damning findings of this study might create trouble for the livestock industry. Giving cattlemen and chicken farmers a way forward instead of a cold shoulder suggests we could turn down the volume of this debate before it ever gets started. We are a long way from anything right now and far more research needs to be done to confirm these findings but we hope Varki keeps blazing his sialic path and better helps us to understand how to enjoy meat products in a healthier way.
-An Interview with Dr. Ajit Varki [voiceofsandiego.org]
-Sialic Acids in Human Health and Disease, a review by Dr. Varki