Last week I came upon a 1998 study finding that the risk of heart attack was 18 times lower in people who donate blood, compared to a matched sample of people who don’t. I ran out to my local Red Cross Blood Drive, and then came home for some follow-up reading. The consensus from a handful of studies on blood donation seems to be far less dramatic, but still worth considering.

Hippocrates thought that women purged blood every month to release their toxic humors, and that men might benefit from an artificially-induced version of menstruation. From ancient times until the 19th centuries, bloodletting was a common medical procedure. Leeches were prescribed for a wide range of ailments.

Bloodletting was thought to be beneficial in healing nearly every disease, from acne and asthma, to cancer and smallpox. Even the loss of blood from a wound was treated by…removing more blood! Bloodletting the already-wounded was thought to reduce inflammation (which is why it was employed prior to surgery as well). Bloodletting wasn’t limited to curing disease either, but was also used as a preventive measure to avoid getting sick. [source]

Modern medical wisdom dismisses these ancient, barbaric practices as fraud, mountebankery and snake oil. But like most medical practices that stood the test of time (if not epemiology), this one held a core of truth.

For centuries, the local barber not only offered close shaves and sharp haircuts, but also provided medical services including bloodletting. In fact, the iconic barbershop pole with its two brass balls and red and white stripes is a vestige of the days when barbers would slit customers’ arms to relieve their ailments.

Epidemiology of Blood Donation

The raw statistics are quite promising. Here is a study that found occasionally donating blood (every three years) is associated with a 50% drop in cardiovascular disease in men. This study finds a 40% reduction in cardiovascular risk, after adjusting for other differences between donor and non-donor groups. These [ref1, ref2] looked at short-term benefits for blood lipid profiles studies following blood donation. These two studies [ref1, ref2] found a slightly lower risk of cancer in blood donors. In a large study of US blood donors, this study found a 30% lower rate for all-cause mortality. This large Italian study found a modest decrease in overall mortality among blood donors.

These were balanced with other studies that found slightly higher cardiovascular risk among frequent blood donors, and several [review] that uncovered no benefit.

The Healthy Donor Effect

It is an obvious point that unhealthy people don’t respond to blood drives. How much of the statistical association with lower health risks is merely self-selection, and how much is causal? Here is a current study claiming that the unadjusted benefit is 18%, and the residual benefit after accounting for the “healthy donor effect” amounts to 7%. These percentages represent reduction in mortality rate for each additional annual blood donation. Based on this unimpeachable source, I have decided to give blood exactly 14.3 times each year, thereby reducing my risk of dying to zero.

Iron

I’m old enough to remember Jack Barry on the B&W TV, the merits of Geritol for “tired blood” — a description of anemia that was intended to suggest that low iron was the primary culprit in an epidemic of chronic fatigue.

Geritol was advertised as an iron supplement. Today’s epidemiology recognizes that anemia is far less common that the opposite, and that too much iron is a risk factor for heart disease, cancer, and Alzheimer’s. (Geritol is still sold today, but its formula has less iron

Modern thinking is that, yes, anemia might limit stamina or even cause fatigue, but people who eat meat and who don’t carry a gene for hemochromatosis are unlikely to be iron-deficient. When iron is in short supply, the body can readily increase its absorption. But the body cannot easily remove excess iron, thus excess iron accumulates in the liver. In fact, too much iron is about four times more common than too little iron in a sample of people over 50 [ref]. The consequences of too little iron are short-term, but the too much iron is a risk factor for chronic disease.

The best-established health risk from too much iron is elevated incidence of diabetes [ref1, ref2, ref3, ref4]. Insulin resistance, in turn, is associated with higher risk of all the diseases of old age. But several studies have found only a weak relationship between excess iron and cancer or mortality risk [ref1, ref2].

Hormesis

Instinct tells me that lower iron is not the only benefit, or even the main benefit from blood donation. First, the body can quickly recover iron lost to blood donation by dialing up the absorption from dietary sources. The effect on the body’s iron stores is likely to be short-term. Second, the evidence for association between high iron and high disease risk is actually weaker than the evidence for benefit from blood donation. So my guess is that this is a hormetic effect. Blood donation is like exercise or a low-calorie diet or low-dose toxins or radiation: it signals to the body that there is danger, which turns on protective mechanisms that go into high gear and overcompensate. (There is an evolutionary explanation for the overcompensation.)

Social and emotional factors have a dominant influence on longevity. It is often overlooked, but connectedness with others, sense of satisfaction and fulfillment, healthy loving relationships are all powerfully correlated with health and life expectancy. Giving blood may be an indicator of pro-social attitudes that prefigure longevity, or it may be an active pursuit of a pro-social behavior that promotes longevity through psychological pathways.

My experience

For several years, Valter Longo has been expounding a theory that an extended fast can reset the immune system. The data on blood donation suggested to me that something similar was happening, and that there might be synergistic benefit from combining a fast with blood donation. I have been doing Longo’s 5-day Fasting-Mimicking Diet every 4-6 weeks, and it happened that I was FMD-ing when I first read about the benefits of blood donation last week.

I found a Red Cross blood drive on the last day of my FMD within 5 miles of my house. I chose discretion over valor, and drove out there rather than deploying the bicycle which is my habitual mode of transit. It had been several years since I have given blood, but I could hardly be surprised that there was 40 minutes of paperwork the Red Cross asked me to read and sign. Reasons for exclusion include not just infectious diseases but travel to many regions of the world, intravenous drug use (ever), homosexual activity (ever), cancer (ever), several congenital diseases….I started to feel nervous that they would ask whether I had been on a semi-fast for 5 days, or discover that I hadn’t had a meal in almost 22 hours. They didn’t ask anything of the sort, and I was able to answer all the questions truthfully. When I had trouble raising the thermometer above 96 degrees and my blood pressure read out at 85/60, they asked if this was usual for me. I offered the excuse that ”I am a marathon runner”, which is a stretch.

Red Cross is strict about the rules, but they really do want our blood. So I slipped through, stretched out on the table and offered up my left arm. The procedure itself took only 15 minutes, and went off without a problem. No light-headedness or weakness–I got up afterward and walked out, hungry and more than ready to re-feed myself after 5 days of minimalist fare. I might have bicycled after all.