Slayer's Den

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Should We Really Be Worried About Heavy Metals?​

California's Proposition 65 wants to keep us safe, but is it instead instilling unnecessary fear and hurting businesses? Get the facts here.​

You’ve probably seen the recent news coverage featuring a story by Consumer Reports regarding the elevated levels of lead and cadmium found in various samples of popular dark chocolate brands.

Sounds scary, right? Unfortunately, these types of reports are designed to instill fear and scare readers into believing they’d better remain subscribers lest they miss out on the next warning.

The truth? Heavy metals such as cadmium and lead are all around us and difficult to avoid if you want to live on planet Earth. Even areas you might consider pristine, like Mount Everest, have heavy metal contamination to the degree that you wouldn’t want to drink the melted snow (1).

Furthermore, the analysis for the dark chocolate considered California’s Proposition 65 (i.e., specifically, the maximum allowable dose level or MADL) as its guide for determining whether the levels present were alarming or not, rather than national or internationally recognized reference intakes (1,2).

For those not familiar with it, Proposition 65, while commendable in some respects, sometimes has unrealistic expectations for various exposure limits and safe intake levels for potentially harmful compounds (3). It’s not uncommon for foods and other items to contain a Proposition 65 warning so that its manufacturer may sell the item in California while avoiding getting sued for failure to disclose.

You may wonder why products sold outside of California have these same warnings. For most manufacturers, it’s simply because it’s easier to have a uniform label rather than one designated only for California.




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There have been instances where Proposition 65 has led to meaningful reductions in the levels of some potentially harmful chemicals. However, there are also instances where there isn’t much a given manufacturer can do to reduce the level of certain chemicals. (In some cases, it may not be possible at all, and in others, it may be difficult due to time and cost.)

Additionally, the proposed MADL is derived from an ill-defined endpoint; is far more conservative than practicable; or isn’t supported with a large body of quality evidence. By specifically relying on Proposition 65 figures for these metals, you’re virtually guaranteeing you’ll get some samples beyond their defined MADL.

It’s not uncommon to find warnings in parking garages, amusement parks, gyms, and even coffee shops (due to the acrylamide present in coffee; levels which are harmless and which California has only recently instructed coffee shops to ignore) (1,2). There’s a long list of foods and consumer products that carry these warning labels to the point that most consumers probably find them of little use.

In any event, if using Prop 65 as a guide for food ingestion and general living, you’d have a rather large supply of things to avoid. In fact, regarding lead and cadmium ingestion limits per day, background levels (i.e., the levels ingested by the average person) already exceed the MADLs set forth by Prop 65 (2). Feel free to slap a Prop 65 warning on yourself!




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Perversely, the foods that may contribute the most of these heavy metals are sunflower seeds, peanuts, soybeans, shellfish, leafy greens (spinach, lettuce, and kale), and potatoes (6-10). However, virtually any fruit or vegetable will contain at least some level of these metals. They’re ubiquitous in our environment. Unsurprisingly, vegetarians have an average cadmium intake nearly three times greater than non-vegetarians (11).

Based on the average concentrations reported by authoritative agencies, a single 30-gram serving of raw spinach (or 40 grams boiled) exceeds the MADL set by Prop 65 for cadmium. How about a plain baked potato? Same.

I hope you weren’t planning on having a 3.5-ounce serving of boiled shrimp. That’s over the MADL for lead. How about some quinoa? I hope it’s less than an ounce. You like peanut butter? Okay, but don’t have more than 6 tablespoons, which is bad if you’re a glutton like me.

How about splurging and having a plain milk chocolate candy bar? You may be over the limit. Shredded Wheat for breakfast? Okay, but if you consume 2 servings, you may be over the cadmium limit. Have a thing for sunflower seeds? A small cup of around 30 grams will put you well over the limit (6,7,10,11).

More seriously, rather than avoiding foods, including otherwise healthy ones, just keep a few things in mind:

1. Always wash your fruits and vegetables thoroughly.
2. Try to mix up your diet and avoid eating large quantities of the same foods daily.
3. Even if a food has higher levels of lead or cadmium, this is only one factor that ultimately determines how much ends up in your bloodstream and tissues (8,12).
4. Eat garlic. It appears to protect against oxidative damage from lead, cadmium, and other metals. The evidence isn’t extremely strong, but if you already enjoy garlic, keep enjoying it (7).
5. Eat regular meals as opposed to fasting (14).
6. When it comes to lead and cadmium, make sure you’re getting adequate amounts of iron, zinc, calcium, copper, vitamin C, and protein. They may either help reduce total body burden or, in some cases, mitigate the adverse effects of these metals (11,13,14).
7. Consider sweating more, whether via exercise or the sauna. This may help reduce levels of certain heavy metals.