Heavy metals in the health context typically means highly toxic metals eg lead, mercury, cadmium. In general the term refers to metals with high densities, but no one would call iron a heavy metal in the context of health.
Just about everything you eat has lead and cadmium and arsenic in it. What is important how much lead/mercury/cadmium/arsenic any particular foodstuff or food supplement contains, relative to other products and your diet as a whole. For example, I might have been slow-poisoned by lead in a magnesium supplement whereas an altnerative product is 221X lower or so— always obtain the certificate of analysis.
I’ve known about lead and cadmium in chocolate for some time now. I never thought I could be consuming enough for it to be an issue, but with recent high blood lead levels, now it makes me wonder a bit.
Still, the whole thing is probably way overblown, it being a matter of setting standards lower and lower. Many natural soils have heavy metals, and the actual linkage between health problems and levels of heavy metals in the body seems to be very poorly understood, short of quite high levels. And with little scientific insight in the context of the rest of the physiological condition. In short... it’s pretty much a guessing game, at least to a point.
Then there is the question of hormesis, whereby most assumptions are rendered highly inaccurate. I don’t know what to think about these claims on heavy metals or about my own blood lead level.
See also: Best Magnesium Supplements Revealed by ConsumerLab which also notes lead contamination in some brands (all have some lead, it's a mater of how much). It’s the wild west out there, so consider asking for the lab analysis.
Consumer Reports found dangerous heavy metals in chocolate from Hershey's, Theo, Trader Joe's and other popular brands. Here are the ones that had the most, and some that are safer.
...For 23 of the bars, eating just an ounce a day would put an adult over a level that public health authorities and CR’s experts say may be harmful for at least one of those heavy metals. Five of the bars were above those levels for both cadmium and lead. Read more about how CR tested dark chocolate (PDF).
WIND: what if the ones with more are more safe, due to hormesis?
The whole thing can be pretty unfair as well: what if a brand changes its sourcing? Once maligned, the brand is hurt. Other brands with lower level can also change sourcing. Then what?
UPDATE: the article is a bit overblown; it uses a cutoff of 0.5 mcg per day, an extreme California standard for pregnant/lactacting women. Eating a leafy green salad might have more than that! The general standard is no more than 15 mcg per day from all sources.
Furthermore, the MgCl hexahydrate I had been using was a whopping 2 mcg per serving (and 3-4 servings!), as compared to about 0.86 mcg for (for example) one ounce of Lindt dark chocolate. If you ate an entire Lindt chocolate bar of 3.5 oz, you'd get 3 mcg of lead intake—not good but that’s an entire bar.
A good summary about this topic came along in an email from...
Rhonda Patrick of FoundMyFitness.com:
- 30+ brands of dark chocolate and cocoa products were tested for contamination with heavy metals, including lead and cadmium.
- Most of the products tested contained quantities of heavy metals that exceed acceptable California Proposition 65 limits
- High blood lead and cadmium levels are associated with cognitive impairment and infertility.
- Elimination of certain heavy metals from the body can be enhanced by lifestyle behaviors such as sauna use, which enhances excretion through sweat.
- Whether the amount of heavy metals found in a serving of dark chocolate is cause for concern – especially for vulnerable groups, like children and pregnant women – is unclear.
Heavy metals are ubiquitous, naturally occurring elements. Heavy metals such as lead, cadmium, aluminum, arsenic, mercury, and chromium occur naturally in the environment. However, most human heavy metal exposure arises from industrial activities that introduce the metals into soil and water supplies. Over time, these metals accumulate in the environment and often find their way into many foods, including fish, meat, fruits, vegetables, tea, spices, processed baked goods, and others.
In short, most of the foods that you eat on a daily basis likely contain some amount of heavy metals.
The clinical significance of daily heavy metal exposure in foods is a matter of debate. Whether heavy metal-rich foods actually pose a significant health risk is unclear. In fact, leafy greens – such as spinach, kale, and chard – are laden with various heavy metals (including aluminum and lead) but are generally considered good for you, providing tremendous benefits for cognition, cardiovascular function, and aging. And there's no indication that people who regularly eat foods rich in heavy metals exhibit greater bioaccumulation of heavy metals. In fact, vegetarians appear to have lower blood levels of heavy metals than omnivores.
That being said, the levels of lead and cadmium in the tested chocolate products were particularly high, with just one serving – an ounce – of most brands exceeding acceptable upper limits.
...Cocoa flavonoids may benefit aspects of human health. However, many beneficial health effects have been attributed to cocoa and chocolate, especially dark chocolate. Cocoa and chocolate have the highest concentrations of flavonoids among commonly consumed foods, with roughly 10 percent of the weight of cocoa powder coming from flavonoids. Robust evidence suggests that cocoa flavonoids improve blood flow, lower blood pressure, promote healthy blood lipid concentrations, lower the risk of cardiovascular disease, protect the skin from sun damage, and improve blood flow to the brain.
WIND: I don’t have a link for the above as it came in an email with (not very smart) no web link. But here is a place to start.