We're oyster farmers, not scientists, so take this all with a grain of salt.
Like many foods, oysters contain cadmium, a heavy metal found in water and soil throughout the world. Our primary exposure to the metal comes from the food we eat. In the average American diet, the most common sources of cadmium are cereals and breads, leafy vegetables, potatoes, legumes and nuts, and stem/root vegetables.(1) (Cigarettes, which you shouldn’t smoke, also contain cadmium.) Cadmium is toxic, and if it builds up in your body it can cause bone and kidney problems, among other health concerns.
That’s the bad news. The good news is that, for most of us, something like 95% of the cadmium we eat is excreted by the body. If you’re looking to reduce your chances of absorbing cadmium, you should make sure you’ve got adequate supplies of iron and zinc. Zinc reduces cadmium absorption, and prevents or reduces the adverse effects of cadmium. Zinc deficiency, on the other hand, can intensify cadmium accumulation and toxicity.(2) And, studies show that people with low iron tend to absorb more of their dietary cadmium than people with adequate levels of iron.
The great news? Oysters are one of the world’s best sources of zinc. (3) And they contain lots of iron, too, as well as copper, vitamin b-12, and omega-3 fatty acids.
When we first learned that oysters contain cadmium, in the mid 2000s, we volunteered to help with studies to determine the actual human health risk. That research, published in 2008, determined that even daily oyster intake does not appear to present health risks. (4)
We’re not trying to give medical advice. (For medical advice, consult your doctor.) We are, in fact, trying to sell oysters, because we firmly believe that this is one of the world’s best, most sustainable, and healthiest foods. We eat oysters several times a week, and our kids eat right alongside us. We’re all doing pretty well, health-wise, and our grandfather, who started the oyster farm seven decades ago, lived to be nearly 101. We firmly believe that shellfish are part of a healthy, balanced diet, and feel good about eating them, selling them, and serving them. (5)
1) Dietary Cadmium Intake and Sources in the U.S., Kijoon Kim and others.
2) Interactions between cadmium and zinc in the organism, M M Brzoska and J Moniuszko-Jakoniuk
3) The Nutritional Value of Shellfish, Faye M Dong, Washington Sea Grant
4) Health Risk Characterization for Consumption of Cadmium in West Coast Oysters, prepared by Integral Consulting Services and Pacific Shellfish Institute for Oregon State University, August 2008.
5) "In a similar study, less cadmium was absorbed from a shellfish diet than from a mixed diet, even though the former containing twice as much cadmium as the latter." From WHO Food Additives Series 46: Cadmium