 When people hear arsenic, they think of it as an acute poison, and indeed a tiny amount, 100 milligrams, could kill you in an hour. That's like the weight of a tenth of a paperclip. But there's also chronic arsenic poisoning, where even a dose 10,000 times as small can be harmful if you're exposed day after day for years at a time. Chief among the concerns is cancer. Arsenic is classified as a Class 1 carcinogen. That's the highest level, things known to cause cancer in humans, alongside stuff like asbestos, cigarette smoke, formaldehyde, plutonium, processed meat, consumption of bacon, ham, hot dogs, and lunch meat. So arsenic is pretty bad stuff, implicated in tens of thousands or even hundreds of thousands of cancer cases worldwide every year. Of course, cancer is just our number two killer. What about heart disease? Long-term exposure to low to moderate arsenic levels was also found associated with cardiovascular disease incidents and mortality, meaning heart attacks and strokes. Arsenic is also considered an immunotoxicant, meaning toxic to our immune system. How do we know that? Well, there's a virus called varicella, which is what causes chickenpox, the first time we get it. Our immune system is able to stamp it down, but not stamp it out. The virus retreats into our nerve cells where it lies in wait for our immune function to dip, and when it does, the virus reemerges and causes a disease called shingles. We've all been exposed to the virus, but only about one in three of us will get shingles because our immune system is able to keep it at bay. But as we get older or immunosuppressed, the virus can slip its muzzle like if you're given arsenic chemotherapy. Shingles is a common side effect because the arsenic drugs not only kill the cancer, but also some of your immune cells, too. But that's at high doses. Might even low doses of arsenic, like the kind we're exposed to in our daily diet, impact our immune function? We didn't know until this study in which thousands of Americans had the levels of arsenic in their urine tested, along with their level of antivirus antibodies, and indeed the more arsenic they had flowing through their bodies, the lower their defenses. And if you're pregnant, arsenic can pass to your baby and may not just increase the risk of miscarriage and infant mortality, but may also affect an infant's immune development and susceptibility to infections early in life, but you don't know until you put it to the test. Infant infections in relation to prenatal arsenic exposure in a study out of New Hampshire, and indeed the more arsenic the mom was exposed to during pregnancy the higher risk of infection during infancy. Though it's unknown whether arsenic-induced changes in gene expression can impact the health of not only your children, but your grandchildren as well. Regardless, arsenic exposure isn't good for mom's own health associated with increasing blood pressure. If arsenic suppresses immune system function, though, then at least maybe as a silver lining you'd get fewer allergies or something, which is kind of an overreaction of the immune system? Apparently not. Those with higher arsenic levels tend to have higher rates of food allergies, tend to not sleep as well, tend to not feel as well. If you ask people how they would rate their health, those reporting excellent or very good tended to have lower levels of arsenic compared to those who just reported good, fair, or poor. They tended to have higher levels. What about diabetes? Here's two dozen population studies on arsenic exposure and confirmed diabetes. Any result over one suggests increased risk for diabetes. Anything below one suggests lower risk, and here are the results. Suggesting an association between ingested arsenic and diabetes, but population studies can't prove cause and effect. While it'd be nice to demonstrate a cause and effect relationship, is it necessary? Look, we know it's a carcinogen. We know it causes cancer. What more do we need to take steps to decrease our exposure?