Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The brain parasite toxoplasma “is responsible for considerable disease and death in the United States.” It is the second leading cause of foodborne-related death in the U.S., after Salmonella. It can invade through the placenta, so can be especially devastating during pregnancy, leading to miscarriages, or blindness, or developmental delay. It can impair cognitive function in adults too, which explains why those who are infected appear to be at increased risk for getting into things like traffic accidents. “Multiple lines of evidence indicate that chronic [toxoplasma] infections “are likely associated with certain psychiatric disorders.” It may even increase the risk of developing leukemia. Okay, okay; how do you prevent it?

Well, the parasite can get into the muscles. So, from food-animals, people can get it “through meat consumption.” But in “a non-food animal like a cat,” you get infected through contact with feces. Thankfully, in cats, the “danger of infection exists only when the animal is actively shedding [the parasite.]” They get it from eating infected rodents. And so, cats that are kept indoors, that don’t hunt, and are not fed raw meat shouldn’t pose a threat—though if feral cats are turning your local playground sandbox into a litter box, that could be a problem. As many as 6 percent of stray cats or those with outdoor access may be actively infected at any one time. They only shed the parasite for a few weeks, though. So, if you adopt a cat at a shelter, it should be safe as long as they didn’t just come in.

Many women have heard about the cat connection, but may be less aware of the risk of foodborne infection. “Only [about one in three] may be aware that [toxoplasma] may be found in raw or undercooked meat. Nevertheless, a high percentage of women indicated that they do…[try to] practice good [hygiene]…such as washing their hands after handling raw meat, gardening [where cats may be pooping,] or changing cat litter.”

What’s the riskiest type of meat? “Cattle are not considered important hosts for [the parasite;]” it’s more pigs and poultry, as well as sheep and goats. The prevalence of infection among factory-farmed pigs varies from 0 to over 90 percent, though, ironically, the likelihood of toxo infection in organic meat may be higher because the animals have outdoor access.

Who undercooks pork and poultry, though? Surprisingly, about one in three Americans may undercook meat across the board, in terms of reaching necessary pathogen-killing temperatures, and a single slice of ham can end up with more than a thousand parasites per slice.

Current meat inspection at the slaughterhouse can’t detect them. There are tests you can do, but there is no widespread testing. The risk from a single serving of meat, though, is really small. The average probability of infection per serving of lamb, for example, was estimated to be 1 in like 67,000. The reason there are 16 times the number of cases attributed to pork is not because pigs are more affected; in the U.S., we just happen to eat a lot more pork chops than lamb chops.

Is there anything we can do if we’re one of the approximately one in four Americans already infected? Well, one of the problems with having these parasites in our brain is accelerated cognitive decline as we age. This study evaluated older adults every year for five years, and the executive function of those testing positive for toxoplasma seemed to drop quicker over time, as did a measure of their overall mental status.

Another thing that’s associated with cognitive decline is reduced folate availability, and the two may actually be related, as recent evidence suggests that toxoplasma may harvest folate directly from our nerve cells, sucking up folate from our brain. So, beyond dopamine production, which is why we think toxo increases the risk of schizophrenia, the parasite may be sucking folate out of our brain. But enough to affect our cognitive functioning? Perhaps so. Here’s a measure of cognitive function across a range of folate concentrations. Among those uninfected, it doesn’t seem to matter whether they have lots of folate or little. They obviously have enough either way. But those who are infected have worse scores at lower levels (higher is worse on this test). The same thing with vitamin B12. So, it’s important to get enough B12 and folate. For B12, the official recommendation is that all people aged 50 or over start taking a vitamin B12 supplement, or eat vitamin B12-fortified foods every day. And, anyone on a plant-based diet should start taking that advice at any age. And folate is found concentrated in beans and greens. So, following my Daily Dozen recommendations will get you more than enough, as, for example, a half-cup of cooked lentils gets you half the way there, as does three-quarters of a cup of cooked spinach.

Please consider volunteering to help out on the site.