 The half-life of lead in the bloodstream is only about a month. That means if you feed people lead for about 100 days, their blood levels go up and up, and then if you stop, the lead levels in the blood start to drop, such that within about 30 days, your lead levels are cut in half. Another month, cut in half again, such that by three or so months, your body is able to remove about 90% from your bloodstream. Now if you're chronically exposed to lead, you can have chronically high lead levels in your blood. More than half a million kids in the US have concernedly high lead levels, and poor people in politically disempowered communities of color are at higher risk regardless of age. But if you don't live in those communities, aren't constantly exposed to lead, why should you care about dietary strategies to lower the lead level in your own blood if your body is already so good at it? Even if you get exposed to lead here and there, three or four months, and 90% of the lead in your blood is gone. Ah, but the question is gone where? More than 90% of lead in our body is stored in our bone. And instead of a few months to get rid of it, how about a few decades? So even if we moved to some like other planet and had zero further exposure to external sources of lead, we still have an internal source of lead leaching the toxic heavy metal into our system throughout our life. But if it's mostly just socked away in our skeleton, what's the big deal? Well, if you were to lose bone, all the trapped lead could come flooding back into your system. For example, when we lose weight, we lose bone, which makes a lot of sense. I mean, heavier people have a heavier skeleton, greater bone mineral density. Their body has to maintain stronger bones to carry around all that extra weight. So if we lose weight, does the levels of lead in our bloodstream go up as our skeleton down sizes? Unfortunately, yes. But only if we lose a lot of weight. I lose 10 pounds or so and not much happens. But lose more like 80 pounds and the lead levels in your blood can rise 250%. And else, can you experience bone loss? Well, osteoporosis, obviously. Women with osteoporosis can lose an average of 3% of their bone mass a year. But even healthy postmenopausal women without osteoporosis may lose a percentage of their skeleton annually. So do the lead levels in women go up when they lose their periods? Apparently so. A study of nearly 3,000 women found a significant increase in lead levels after menopause, adding evidence that bone lead is in fact mobilized into the blood. A major implication is that even low-level lead exposure over a relatively long time may result in increased body burdens of lead, which would be releasable in toxicologically significant amounts during physiological states where your bone is in flux. Not just osteoporosis, but most seriously during pregnancy and lactation. Now most of the calcium the baby gets comes from increased maternal absorption of dietary calcium. The mother's gut starts absorbing 60% or 70% more calcium in the second or third trimester to build the baby's skeleton. That's why women's dietary calcium requirements are not increased by pregnancy or breastfeeding. Your body is not stupid when it realizes it needs more calcium. It just absorbs more calcium. Now when that isn't enough, you do end up dipping into the calcium stored in your bones, but not a problem after it's all over. Your body puts the calcium back into your skeleton, such that six months after delivery, your bone mineral density is right back where you started. That's why even women who breastfeed for a long time well past those six months in pregnancy, after pregnancy, after pregnancy, after pregnancy end up with no compromise to their bone mineral density later in life, whether measured in their wrists, spine, or hips. So what if your body makes a withdrawal from the bone bank during pregnancy and lactation if it ends up just depositing it all back? Because of the lead. When your body dissolves some of your bone to borrow that extra calcium, it releases the lead that's locked in there at the worst possible moment right when your baby is most vulnerable. That's part of lead's toxic legacy. What can we do about it? We'll find out next.