Why does flaxseed have a prop 65 warning?

December 19, 2025 •

3 min read

According to a ConsumerLab report, one-third of flaxseed products tested contained high levels of cadmium, which is the primary reason why does flaxseed have a Prop 65 warning. This informational label can be concerning, but understanding the specifics is key to making informed dietary choices without unnecessary alarm.

Quick Summary

Flaxseed carries a Prop 65 warning primarily due to naturally occurring cadmium absorption from soil. The warning informs consumers of potential exposure, not imminent danger, allowing for informed purchasing decisions.

Key Points

Cadmium is the Cause: The primary reason for a Prop 65 warning on flaxseed is the presence of the heavy metal cadmium, absorbed naturally by the plant from the soil.
Not an Unsafe Product: A Prop 65 warning is a 'right-to-know' label mandated by California and does not mean the product is unsafe or violates federal food standards.
Levels Can Vary: Cadmium levels in flaxseed can fluctuate significantly based on soil composition, region, and weather during growth.
Oil vs. Seed: Cadmium is largely contained within the seed's solids; therefore, flaxseed oil typically does not contain significant levels of cadmium, while whole and ground flaxseed can.
Look for Tested Brands: Consumers can reduce risk by choosing reputable brands that test for heavy metals and publish the results, as independent testing has shown variability.
Diversify Your Diet: To minimize exposure to any single contaminant, it is wise to incorporate a variety of seeds and grains into your diet rather than relying on one source.

Understanding California's Proposition 65

California's Proposition 65, officially the Safe Drinking Water and Toxic Enforcement Act of 1986, requires businesses to warn Californians about significant exposure to chemicals causing cancer or birth defects. This applies to businesses with 10 or more employees and mandates a "clear and reasonable" warning for products exceeding specific thresholds of listed chemicals. The list, updated annually by OEHHA, includes over 900 chemicals.

A Prop 65 warning is a 'right-to-know' measure and does not mean a product is unsafe or violates federal food safety standards. Warning levels are often stricter than federal guidelines, leading to warnings on everyday foods with trace, naturally occurring chemicals like acrylamide in coffee or cadmium in certain grains.

The Main Culprit: Cadmium Absorption

The primary reason for a Prop 65 warning on flaxseed is the presence of cadmium, a heavy metal.

Flax plants absorb heavy metals from soil, a process known as phytoremediation. This can result in higher cadmium levels in seeds compared to other crops, even in normal soil. Cadmium levels vary based on soil type, geography, farming practices, and weather. Cadmium is known to cause birth defects and reproductive harm in California. While the body can handle trace amounts, high intake over time is linked to kidney/bone injury and cancer.

Can Flaxseed Be a High Source of Cadmium?

Independent tests have shown significant variation in cadmium levels in flaxseed products, with some exceeding California's Prop 65 limits. Cadmium is mostly in the seed solids, making flaxseed oil generally not a cadmium concern.

Potential Secondary Concern: Cyanogenic Glycosides

Flaxseed contains cyanogenic glycosides, which release small amounts of hydrogen cyanide during digestion, similar to some other seeds. The body can neutralize these small amounts in typical servings. Raw or unripe seeds are more toxic and should be avoided. Cooking can break down these compounds.

A Comparison of Flaxseed Products

This table compares whole flaxseed, ground flaxseed meal, and flaxseed oil:


Feature	Whole Flaxseed	Ground Flaxseed Meal	Flaxseed Oil
Heavy Metal Risk	Carries the risk of cadmium absorbed from soil.	Also carries the risk of cadmium from soil.	Very low to no risk, as cadmium stays with the seed solids.
Cyanide Compounds	Contains cyanogenic glycosides, harmless in small doses.	Same as whole seeds, compounds are neutralized by the body.	None, as compounds are not extracted into the oil.
Omega-3s (ALA)	Good source, but less bioavailable as seeds pass undigested.	Excellent source; grinding makes ALA more readily available.	Highest concentration of ALA.
Fiber Content	High in both soluble and insoluble fiber.	High in both soluble and insoluble fiber.	Contains no dietary fiber.
Lignans (Antioxidants)	High concentration in the seed coat.	High concentration; grinding makes lignans more available.	Almost no lignans, as they are not oil-soluble.
Shelf Stability	Most stable, can be stored at room temperature.	Prone to oxidation once ground; must be refrigerated.	Must be cold-pressed and stored in opaque, refrigerated bottles.

How to Reduce Heavy Metal Exposure from Flaxseed

To minimize potential heavy metal exposure while enjoying flaxseed's benefits:

Choose Reputable Brands: Look for brands that test for heavy metals and publish results. Independent reports, like from ConsumerLab.com, can help.
Diversify Your Diet: Avoid relying too heavily on one food item. Varying your intake of grains and seeds balances risks.
Consider Whole vs. Ground: Grinding whole seeds yourself and storing the meal properly maintains freshness.
Support Detoxification: A balanced diet with fiber, iron, and vitamin C can support the body's natural processes.

Conclusion

Flaxseed carries a Prop 65 warning mainly due to potential cadmium from soil absorption. This warning is a disclosure under California law, not a prohibition. For most, flaxseed's nutritional benefits likely outweigh the minimal risk from trace cadmium. By choosing reputable brands, diversifying your diet, and understanding the warning's context, you can safely enjoy flaxseed.

For Further Reading:

California's Official Proposition 65 Warnings Website: https://www.p65warnings.ca.gov/

Frequently Asked Questions

The main chemical is cadmium, a heavy metal that flax plants naturally absorb from the soil. This heavy metal is on California's Prop 65 list as a cause of cancer and reproductive harm.

No, the warning does not mean flaxseed is unsafe. It is a California 'right-to-know' label indicating that a product exposes consumers to a listed chemical above a certain threshold. It is not a declaration of toxicity in the amounts typically consumed.

Cadmium is a naturally occurring heavy metal in soil. Flax plants are known to be particularly efficient at absorbing it, a process called phytoremediation. Therefore, the cadmium ends up concentrated in the seeds.

Flaxseed also contains cyanogenic glycosides, which can form small amounts of cyanide. However, the human body can safely neutralize the trace amounts found in typical servings. Raw or unripe flaxseeds should be avoided as they can be more toxic.

Prop 65 is a California law, but the warnings are often placed on products sold nationwide. While the law doesn't apply outside California, it's a useful indicator that trace chemicals might be present, allowing you to choose tested products if concerned.

No, ground flaxseed meal is not necessarily safer. Cadmium is present in the solids of the seed, so both whole and ground flaxseed carry a similar risk. The key is the source and testing of the product.

To choose a product with lower heavy metal levels, look for brands that voluntarily test their products and publish the results. Checking independent lab reports, like those from ConsumerLab, can also help.

Generally, no. Cadmium is largely attached to the solid components of the seed and does not get extracted into the oil. Therefore, flaxseed oil is not a significant source of cadmium.