Microscopic organisms — bacteria, fungi, protozoa, and viruses — are extremely abundant on the planet; the estimated number of bacteria alone is ~5 x 10^30, and their total content of carbon, nitrogen, and phosphorus weighs more than all plants put together.(1)
Many of these organisms are capable of either living in or on humans, and some of them cause disease when they do so.
Humans and indeed all organisms possess more or less elaborate means of protecting themselves from microbial invaders. We normally think that certain sites of our bodies are meant to be off-limits to microbes, and other sites to be loaded with them. The human mouth, gut, and skin are loaded with microbes, but generally other body sites are supposed to be sterile — the blood, for instance.
But scientists have recently discovered that the blood of healthy people (blood donors) contains an abundance of bacteria and viruses.(2)
These microorganisms get into the blood presumably through breaches in the tight junctions in the gut, through the lungs, and the skin.
What they’re doing there is anyone’s guess just now. It was formerly thought that any bacteria in the bloodstream caused disease — sepsis — but apparently not.
The blood of patients with cardiovascular disease is higher in bacteria than in healthy controls, from 40- to 70-fold higher, which suggests that there could be a link between these bacteria and heart disease.(3) It’s already known that periodontal disease increases the risk of heart disease, apparently even when controlling for socioeconomic status.(4) It could be that the pockets of oral infection shed bacteria into the bloodstream, leading to increased heart disease risk.
A new book by Michael Lustgarten, PhD, Infectious Burden: The Cause of Aging and Age-Related Disease, makes the case that these new discoveries show that microorganisms are intimately involved in aging and in fact may cause aging. (The book is free for the next several days.)
Lustgarten shows that microbes are involved in many diseases that increase with age, such as heart disease, cancer, and Alzheimer’s.
As people get older, their susceptibility to infections increases due to declining immune function.
So is the increased number of infections due to aging, or do the bacterial, viral, and fungal agents of infection cause aging?
Certainly, finding that bacterial numbers are greatly increased in heart disease, and that bacteria (Treponema) and fungi may be important to Alzheimer’s disease is important.
Do these increased numbers result from a lack of immunity?
In most infections, the agents causing the disease are pathogens, i.e. they are capable of causing disease when they invade a host. Think of Salmonella, for instance, which may be normal flora in some animals but causes serious illness in humans.
In other infections, the organisms are opportunistic, causing disease only in debilitated subjects (e.g. pneumocystis pneumonia in AIDS patients), or causing disease when they get somewhere they don’t belong (e.g. E. coli and urinary tract infections).
Therefore, it’s not a simple matter to say when an organism is causing a disease and when it just happens to be there. Everyone has bacteria on their skin, for instance, but few people have skin infections.
Likewise, if healthy people have bacteria in their bloodstreams, but no apparent illness, what’s going on?
So, we already know that elderly people are subject to increased infections; we may yet confirm that microorganisms are causative in heart disease and Alzheimer’s. But are these microbes causing aging, or these diseases, or is a great part of their power that they hit aging and/or debilitated people?
Older people have increased amounts of iron in their bodies, and more of it is unregulated, i.e. not bound to ferritin. And iron increases infections. Microorganisms require iron for growth, and usually have a hard time getting it; having a lot of it around is just giving pathogens what they need.
So if bacteria and fungi are in the brains of Alzheimer’s patients, what’s causing the Alzheimer’s, iron or pathogens?
Alzheimer’s has also been characterized as type 3 diabetes, and in diabetes, blood sugar levels are high, again providing pathogens with a required nutrient. Diabetics have up to a 10-fold increased incidence of urinary tract infections for that reason: glucose in the urine feeds bacteria.(4)
My judgment on whether microbes cause aging is that the case is very provocative but not proven.
In his book, Dr. Lustgarten makes a number of suggestions as to what to do about microbes as they relate to aging. For example, he suggests using soaps that do not raise the pH of skin (most of them do), so as to maintain the skin barrier function. (He didn’t suggest going all the way and not using soap at all. That’s for us radicals.)
He also suggests ways to maintain the barrier function of the gut, which is indeed important, as well as ideas for promoting good oral health.
However, bacteria are everywhere, and while you can keep the numbers of those that get into the body way down, you can’t keep them out entirely.
Good oral hygiene has been shown to decrease the number of incidents of pneumonia in the elderly who live in nursing homes, but will it do the non-elderly and reasonably healthy any good?
It’s a good question. While infected gums are associated with heart disease, is this just an association? People with infected gums and missing teeth are very likely to neglect their health in other ways.
And if healthy people have bacteria in their blood but no heart disease or other illness, what does that mean? Will keeping bacteria out of your body help you at all?
We simply don’t have all the answers yet.
My take on prevention is that a sound and healthy immune system is the best defense. While you don’t want huge numbers of even allegedly non-pathogenic bacteria pouring into your bloodstream, it appears that it may be next to impossible to keep them all out.
A healthy immune system is the result of everything else that makes for good health: diet, exercise, sleep, supplements, etc.
Infectious Burden presents a provocative thesis, and we will undoubtedly learn much more about the role of microbes in aging in the years to come.