Bone broth is a liquid preparation made by slow-simmering animal bones and connective tissues, often for 12 to 24 hours, to extract their components. This traditional cooking method has become a popular dietary staple. However, the lengthy preparation process has raised a significant public health question. The central controversy centers on the fear that this prolonged simmering might cause the concentration of harmful substances, specifically heavy metals, which could potentially pose a cancer risk. This concern requires an examination of the broth’s components and the scientific evidence regarding its contaminant levels.
Nutritional Components of Bone Broth
The popularity of bone broth stems from the valuable compounds extracted during the long cooking process. Collagen, the most abundant protein in animal bones and connective tissue, breaks down into gelatin when heated. This gelatin is a source of several amino acids that the human body uses for various functions.
The three most prominent amino acids are glycine, proline, and glutamine. Glycine supports sleep quality and detoxification pathways, while proline is a component of cartilage and skin structure. Bone broth also contains trace minerals, such as calcium, magnesium, and phosphorus, drawn out of the bone matrix. The exact nutritional profile, however, is highly variable, depending on the type of bone used, the cooking time, and the use of acidic ingredients like vinegar.
The Primary Concern – Heavy Metals and Toxins
The mechanism that generates the most serious health concerns involves the way animal bodies store environmental contaminants. Bones are known to be a long-term storage site for certain heavy metals, particularly lead and cadmium, which are absorbed from the animal’s environment throughout its life. As an animal ages, these heavy metals accumulate within the mineral matrix of its skeletal system.
The hypothesis is that the same prolonged, low-heat simmering process designed to extract beneficial collagen and minerals also efficiently mobilizes these stored toxins. The addition of an acid, such as apple cider vinegar, often recommended to maximize mineral extraction, can also significantly increase the leaching of metals from the bone into the liquid. This storage and leaching theory formed the basis for the initial fears regarding the safety of consuming bone broth regularly.
Examining the Carcinogenic Link – The Evidence
The direct question of whether bone broth increases cancer risk is tied to the measurable concentration of heavy metals in the final product. Early studies, such as one conducted in the United Kingdom, found that broth made from organic chicken bones did contain lead, with concentrations up to ten times higher than the plain water used for cooking. This initial finding sparked widespread concern and led to the recommendation that doctors should consider the risk of lead contamination when advising patients about bone broth diets.
However, subsequent and more comprehensive scientific investigations have provided a clearer picture of the actual risk. A 2017 study that examined metal extraction from bones concluded that the levels of toxic metals like lead (Pb) and cadmium (Cd) found in both commercial and homemade broths are minimal. The concentrations of these heavy metals were measured in the range of a few micrograms per serving.
Researchers determined that the risks associated with ingesting these trace amounts of heavy metals from bone broth are low. The measured levels generally fall well below the established safe daily intake limits set by international regulatory bodies. While lead is a known carcinogen and neurotoxin, the current scientific consensus suggests that consuming bone broth does not introduce a significant exposure risk that would substantially increase the likelihood of cancer in the average person.
Mitigating Risk Through Sourcing and Preparation
Consumers who wish to minimize even the trace exposure to heavy metals can adopt specific sourcing and preparation methods. Toxins accumulate in animals over time, so effective strategies focus on reducing the initial contaminant load and limiting extraction:
- Select bones from young, healthy animals.
- Source bones from grass-fed, organically raised animals, which are exposed to fewer environmental contaminants throughout their lives.
- Limit the cooking time to under 8 to 12 hours, as longer simmering increases the leaching of heavy metals.
- Use bones from non-porous joints and knuckles rather than high-porosity marrow bones, where lead is most heavily stored.