Glucosamine and Shellfish Allergy

Glucosamine is a natural substance that plays an important role in the formation and repair of healthy cartilage. It is a popular dietary supplement that's often taken in combination with chondroitin sulfate. Glucosamine is usually made from the shells of shellfish, such as shrimp and crab, and some believe taking the supplement may trigger a reaction in those with a true shellfish allergy. However, this is a controversial topic.

Glucosamine as a Dietary Supplement

Glucosamine is available to purchase by itself, in combination with chondroitin sulfate, or in combination with several other compounds as a nutritional supplement. Glucosamine is sometimes used for the treatment of osteoarthritis, among other conditions, although some research suggests it may be beneficial, clinical trials have not categorically proven these supplements to be beneficial for the joints. Based on results in what is known as the GAIT trial, the American College of Rheumatology recommends against the use of glucosamine to treat osteoarthritis.

Unfortunately, nutritional supplements are not subject to the same stringent guidelines that prescription drugs are, and formulations can vary considerably. There are three primary forms that are available (glucosamine sulfate, glucosamine hydrochloride, and N-acetyl-glucosamine), but what is listed on the bottle does not necessarily correlate with what's inside. Herbal studies have found that the amount of active ingredient in these supplements can vary from zero to 100% of what's listed.

Glucosamine and Shellfish Allergies

Glucosamine is often made from the shells of shrimp, crab, and lobster, so people with shellfish allergies have often been advised against taking this supplement. The topic is a bit controversial.

On the one hand, there was one report of a severe, immediate hypersensitivity reaction that was precipitated by glucosamine in a shellfish-allergic person in 1999. There have also been reported cases that have suggested a link between products containing glucosamine and chondroitin and asthma attacks.

However, according to the American Academy of Allergy, Asthma, and Immunology, it is a misconception that people who have shellfish allergies cannot take glucosamine. There is currently little evidence that glucosamine contains shellfish proteins, the parts of shellfish that are responsible for causing symptoms of food allergies. A few small studies have supported this. 

A 2006 study looked at 15 people who were confirmed to be shrimp-allergic by both skin tests and shrimp-specific IgE assays (blood tests). All 15 of those participants tolerated a supplement of the shrimp-derived glucosamine-chondroitin (1500mg of glucosamine) both initially and after 24 hours (to rule out a delayed reaction).

Given the small number of people studied to date, it would be prudent for people with shellfish allergies to check with their healthcare providers prior to taking glucosamine. Consider asking for a referral to an allergist, who may suggest providing a medically supervised oral challenge to glucosamine.

What Foods Are Considered Shellfish?

There are two main categories of shellfish invertebrates. These include crustaceans and mollusks.

• Crustaceans: This category includes shrimp/prawns, lobster, crab, crayfish (crawfish), and yabbies.
• Mollusks: This category includes oysters, mussels, clams (quahogs), limpets, octopus, snails (escargot), squid (calamari), cuttlefish, sea cucumber, abalone, sea slugs, whelks, cockles, and surimi (imitation shellfish found in sushi)

Foods That May Contain Shellfish

If you are allergic to shellfish, you need to be wary of foods that use shellfish components. For instance, while it's not a problem for the majority of people, pet foods often contain some amount of shellfish. If you are very allergic to shellfish, you may wish to have someone else feed the cat his favorite seafood medley. ​Know which ingredients may contain shellfish and learn how to eat at a restaurant when you have a shellfish allergy. 

Allergy vs. Food Intolerance

It is important to distinguish whether you have a true allergy to shellfish or, instead, a food intolerance. The difference between these reactions determines the type of symptoms that you may experience. With a food intolerance, you may feel very ill, and medical attention may be needed due to dehydration from vomiting or diarrhea. In contrast, with an allergy, you could go into anaphylactic shock, a medical emergency that can be fatal without treatment.

Shellfish Allergy and Food Dyes

Though concern has been raised in the past over a relationship between shellfish allergies and reactions to food dyes and radiocontrast dye, it's currently thought that it's okay to have radiocontrast dye unless you are specifically allergic to the dye itself.

Glucosamine Allergy

Some people may have a specific allergy to glucosamine, even if they don't have a shellfish allergy. Moreover, people with chronic liver disease can develop toxicity from glucosamine and should avoid it unless being given under your healthcare provider's direction.

A Word From Verywell

Though it appears that most people with a shellfish allergy could tolerate glucosamine, discuss it with your healthcare provider before taking the supplement.