 If you took a drop of blood and smeared it between two pieces of glass and looked at it under a microscope, it might look something like this. A whole bunch of little round red blood cells, and then this big white blood cell. Red blood cells carry oxygen, and white blood cells are our immune system foot soldiers. We make sure now 50 billion new ones a day. In response to inflammation or infection, that number could shoot up to 100 billion or more. In fact, that's what pus is largely composed of millions and millions of white blood cells. Testing how many white blood cells we have at any given time our white blood cell count is one of the most common laboratory tests doctors order. We order it hundreds of millions of times a year. So, for example, if you end up in the emergency room with abdominal pain, having a white blood cell count above about 10 billion per quart of blood may be a sign you may have appendicitis. Most Americans fall between 4.5 and 10. But most Americans are unhealthy. Just because 4.5 to 10 is normal doesn't mean it's ideal. It's like having a normal cholesterol level in a society where it's normal to die of heart disease, a number one killer. The average American is overweight, so if your weight is quote-unquote normal, that's actually a bad thing. In fact, having excess fat itself causes inflammation within the body, so no surprise, those who are obese walk around with 2 billion more white cells per quart in their blood. So maybe obese individuals should have their own normal values. Someone with a 47-inch waist walking into an emergency room with a white count of 12, 13, 14 may not have appendicitis or an infection. That may just be their baseline, normal level given all the inflammation they have in their body from the excess fat. So normal levels are not necessarily healthy levels. It's like smoking. If you take identical twins and one smokes and the other doesn't, the smoker is going to end up with a significantly higher white cell count. In Japan, for example, as smoking rates have steadily dropped, so has the normal white count range. Such that about 8% of never-smoking men would now be flagged as having abnormally low white counts if you used to cut off like 4. But that's because most people were smoking before when they set that cut off, so maybe 3 would be a better lower limit. The inflammation caused by smoking may actually be one of the reasons cigarettes increase the risk of heart attacks, strokes, and other inflammatory diseases. So do people have lower white counts, have less heart disease, cancer, and overall mortality? Yes, yes, and yes. People with lower white blood cell counts live longer. Even within the normal range, every one-point drop may be associated with a 20% drop in the risk of premature death. This is a log scale, so there's like an exponential increase in risk as white count goes up, even within the so-called normal range. This is for men, this same is found for women. The white blood cell count is a widely available inexpensive measure of systemic inflammation. At around age 85 in this study, half of women who started out with white blood cell counts under 5.6 were still alive, whereas 80% of those that started out over 7 were dead. And 7, 8, 9, 10 would be considered normal. Being at the high normal range may place one at three times the risk of dying from heart disease compared to being at the lower end. Same length found for African American men and women. Same in middle age. Same at age 75. Same at age 85. Same even in our 20s and 30s. A 17% increase in coronary artery disease incidence for every single point higher. The higher your white count, the worse your arterial function and the stiffer your arteries. So no wonder white blood cell count, WBC count, is a useful predictor of artery disease in your heart, brain, legs, and neck, and high blood pressure. Even diabetes? Even diabetes! According to a compilation of 20 different studies. Everything from fatty liver disease to having an enlarged prostate. And having a higher white blood cell count is associated with an increased risk of dying from cancer as well. And these are all within the normal range. So what would the ideal range be? I'll cover that next.