To the Editor: Seafood is not only consumed as food, but also as dietary supplements and complementary medicines. Examples are capsules of freeze-dried oysters and mussels, or freeze-dried extract of shellfish meat, sold as reputed antihypertensives, cardioprotectants, and anti-inflammatories, among other medical claims. However, oysters and mussels can become dangerously toxic after they ingest poisonous microscopic algae. If these molluscs are sold as food in Australia, they are subject to the Food Standards Code,1 under which their sale is prohibited if biotoxin levels per kilogram of wet shellfish meat exceed 800 g of paralytic shellfish poisons, 200 mouse units of neurotoxic shellfish poisons, 200 g of diarrhoetic shellfish poisons, or 20 mg of amnesic shellfish poisons.

Shellfish capsules can be simply manufactured by milling dried meat and encapsulating the powder, a process unlikely to degrade shellfish biotoxins, which are stable to heat, pressure and freeze-drying. 2,3 Such capsules may then become subject to regulation by the Australian Therapeutic Goods Administration (TGA), which distinguishes therapeutics from food, on the basis of whether there is a “tradition of use as a food in the form presented”, especially if there is an associated health claim. Such complementary medicines can be either “registered” or “listed”. Registered medicines require extensive safety, quality and efficacy data. Listed medicines are considered to pose a lower risk than registered medicines, and regulations allow product sponsors to “self-assess” products. Listing is a route commonly taken for complementary medicines. A pertinent example is the TGA listing of therapeutic goods containing dried green-lipped mussel (Perna canaliculus).4

Where manufacturers of shellfish capsules have undertaken the responsibility of ensuring product safety, they invariably adopt existing biotoxin testing protocols developed for food safety. However, as the allowable biotoxin level is based on wet weight, and the dry weight of bivalve shellfish is only 10%–15% of the wet weight,5 safety limits for shellfish meat as food are incorrect by an order of magnitude, and potentially more for capsules containing extracts of shellfish meat.

While important for acute exposure to these toxins, this may be even more relevant in chronic exposure. Okadaic acid, the cause of diarrhoetic shellfish poisoning, is a tumour promoter,6 and epidemiological studies suggest that rates of cancer have increased in regions with regular dietary exposure to low levels of this toxin.7 Capsules are available that contain 500 mg of dried shellfish meat, which may equate to 5 g of wet shellfish meat.5 Unlike a shellfish meal, which may be considered equivalent to a single acute exposure, recommended doses for shellfish capsules can be as many as five capsules a day for many weeks, if not months, therefore magnifying the risk of chronic exposure. It is known that different classes of biotoxins can co-occur in shellfish, adding to the potential hazard outlined here.8 Further complications arise because some shellfish capsules include other natural extracts (such as ginseng) or pharmaceutical formulations that might affect toxin uptake.

While this situation needs to be subjected to risk assessment, testing products in accordance with an inappropriate standard can make them seem safe when they might not be. This is especially so for products which are usually self-prescribed, and where patients can exceed recommended doses in the belief that more is better. For products such as shellfish capsules that straddle the food/therapeutic divide, it is better for manufacturers to test the final consumer product and not the raw supply.