Joint health nutrition for aging pets: weight and omega-3s

For an older dog or cat with stiff joints, the dietary change with the strongest evidence is also the least exotic: keeping the animal lean. After that, omega-3 fatty acids from fish oil have better support than any other joint supplement. Glucosamine and chondroitin, the products most often bought for joints, have the weakest evidence of the common options.

How common joint disease is

Osteoarthritis is the most common joint disease diagnosed in dogs. In UK primary-care practices, about 2.5% of dogs were diagnosed with limb osteoarthritis in a single year. Dogs older than eight, heavier dogs and breeds such as Labradors and Golden Retrievers were more likely to be diagnosed. A diagnosis rate is not the same as the true rate of disease, since many stiff dogs are never examined for it.

In cats the gap between disease and diagnosis is wider. When researchers reviewed radiographs of 100 cats older than 12, 90% showed degenerative joint disease. Few limp. An older cat that has stopped jumping onto furniture, or grooms less, deserves a check for joint pain before the change is put down to age.

Body weight comes first

The clearest evidence comes from a lifetime study of 48 Labrador Retrievers that ran for well over a decade, from eight weeks of age until each dog died. Littermates were paired, and one dog in each pair was fed 25% less than its partner for life, on the same diet. Radiographic signs of hip osteoarthritis appeared at a median of 6 years in the freely fed dogs and 12 years in the restricted dogs. The leaner dogs also lived longer, with a median lifespan 1.8 years longer, and the onset of late-life disease, osteoarthritis in particular, was delayed.

That was a study of prevention in young dogs, but the principle carries over to an arthritic senior. Less weight, less load. A vet can confirm whether an animal is overweight using a body condition score; the body condition score guide explains how the scale works. Weight loss in an older animal should be slow and planned, because losing muscle along with fat works against mobility.

Omega-3 fatty acids from fish oil

The omega-3 fatty acids EPA and DHA from fish oil have been tested in several controlled trials in dogs with osteoarthritis, mostly using therapeutic foods enriched with fish oil. In one double-blinded trial, dogs on a fish-oil-enriched food bore more weight on their worst leg after 90 days; 82% improved on force-plate measurements, against 38% on a standard food. The effect was modest, but it was measured objectively rather than only by owners.

Dose matters. When a therapeutic food's EPA and DHA content was raised to about three times the baseline level, lameness and weight bearing improved further, while doubling it did not produce a significant difference. A 2022 systematic review of 72 trials concluded that omega-3-enriched diets and omega-3 supplements had clear evidence of pain relief in osteoarthritis. Nearly all of that evidence is from dogs; only three of the trials were in cats.

Two practical points follow. First, a supplement dose should be based on its EPA plus DHA content, not the total fish oil on the label, and set with the vet for the animal's weight and any medication. Second, flaxseed oil is not a substitute: it is a good source of the plant omega-3 ALA, but the best dietary sources of EPA and DHA are oily fish, krill oil and algae oil, according to the Merck Veterinary Manual.

Glucosamine and chondroitin

These are the best-known joint supplements. The evidence for them is poor. The same 2022 review, which scored trials for quality as well as outcome, found a very marked lack of effect for glucosamine and chondroitin products on osteoarthritis pain. Its authors recommended that they no longer be recommended for pain management in dogs and cats.

An owner who still wants to try them should treat them as an extra. They are not a substitute for weight control, omega-3s or pain relief prescribed by a vet.

Green-lipped mussel, cannabidiol and turmeric

Green-lipped mussel (Perna canaliculus) contains omega-3 fatty acids, and the 2022 review grouped mussel products with fish oil among the omega-3 diets and supplements that showed benefit. Cannabidiol (CBD) also showed evidence of pain relief in recent dog trials, though to a lesser degree than omega-3s. Product quality varies and legal status differs between countries, so any CBD product should be discussed with the vet first. Turmeric results were conflicting, with negative, ambiguous and positive trials, and its effect remains unconfirmed.

The rest of the diet

Muscle matters too. In the Labrador lifetime study, high fat mass and declining lean body mass both predicted death. An older animal needs enough good-quality protein to hold on to muscle, unless a vet has advised otherwise for kidney disease.

Activity usually falls with age and arthritis, so calorie needs fall too, often before the owner notices the weight creeping up. Feed to body condition rather than to the amount on the bag, and weigh the animal every month or two.

There is no good evidence that extra vitamins on top of a complete diet help joints. Vitamins A and D are toxic in excess. Coconut oil contains no omega-3s and adds calories an arthritic animal does not need.

A practical order of priorities

1. Have a vet assess pain and body condition, and treat pain properly. Nutrition supports pain management; it does not replace it.
2. Bring an overweight animal down to a lean body condition slowly, keeping muscle.
3. Add omega-3s from fish oil, either as a joint-support therapeutic food or as a supplement dosed on EPA and DHA content.
4. Keep daily activity regular and moderate, suited to what the animal can manage.
5. Be skeptical of products with little evidence, including glucosamine and chondroitin, before spending money on them.

Sources

1. Prevalence, duration and risk factors for appendicular osteoarthritis in a UK dog population under primary veterinary care. Scientific Reports, 2018.
2. Radiographic evidence of degenerative joint disease in geriatric cats: 100 cases (1994-1997). Journal of the American Veterinary Medical Association, 2002.
3. Lifelong diet restriction and radiographic evidence of osteoarthritis of the hip joint in dogs. Journal of the American Veterinary Medical Association, 2006.
4. Diet restriction and ageing in the dog: major observations over two decades. British Journal of Nutrition, 2008.
5. Evaluation of the effects of dietary supplementation with fish oil omega-3 fatty acids on weight bearing in dogs with osteoarthritis. Journal of the American Veterinary Medical Association, 2010.
6. Dose-titration effects of fish oil in osteoarthritic dogs. Journal of Veterinary Internal Medicine, 2010.
7. A 2022 systematic review and meta-analysis of enriched therapeutic diets and nutraceuticals in canine and feline osteoarthritis. International Journal of Molecular Sciences, 2022.
8. Nutritional requirements of small animals. Merck Veterinary Manual.