Safety of three dietary supplements -- lutein, evening primrose oil, and garlic -- to the diets of horses, dogs, or cats has been assessed by a new National Research Council report, requested by the Center for Veterinary Medicine of the U.S. Food and Drug Administration. The report findings suggest that the addition of the above supplements may cause significant adverse health effects. Because of inadequate data, a safe upper limit for lutein, evening primrose oil, or garlic cannot be clearly defined. Therefore, only historical safe intakes (HSI) and estimate presumed safe intakes (PSI) based on available research findings have been used in the report. The committee added that current regulations addressing animal dietary supplements are in "disarray."
The Committee also stressed that "safety in humans does not guarantee safety in animals. For example, excess garlic intake can cause hemolytic anemia in horses, dogs, and cats, but this adverse effect has not been reported in humans".
Lutein and zeaxanthin are xanthophyll carotenoids found particularly in dark-green leafy vegetables and in egg yolks. They are widely distributed in tissues and are the principal carotenoids in the eye lens and macular region of the retina. Human studies indicate that these compounds can play a protective role in the eye. Some observational studies have also shown these xanthophylls may help reduce the risk of certain types of cancer, particularly those of the breast and lung. Emerging studies suggest as well a potential contribution of lutein and zeaxanthin to the prevention of heart disease and stroke. Canine studies show that lutein enhances immune system in dogs.
Garlic prevents cold and flu symptoms through immune enhancement and demonstrates anticancer and chemopreventive activities. In addition, aged garlic extract possesses hepatoprotective, neuroprotective, antioxidative activities, whereas other preparations may stimulate oxidation. Aged garlic extract (AGE) has been shown previously to have moderate cholesterol-lowering and blood pressure–reducing effects. AGE exerts selective prevents clot formation, platelet functions that may be important for the development of cardiovascular diseases such as myocardial infarction and stroke.
Evening primrose oil contains gamma-linolenic acid (GLA), an omega-6 fatty acid that the body converts to a hormone-like substance called prostaglanding E1 (PGE1), which has anti-inflammatory properties. Some evidence supports the fact that GLA- and DHA-enriched diets reduce inflammatory signs in canine atopic dermatitis and papulocrustous dermatitis in cats, as well as for may be an aid in prophylaxis of endotoxemia in horses.
The daily PSI and HSI, given in milligrams per kilogram of body weight (mg/kg BW), determined by the committee for the three dietary supplements are:
Evening Primrose Oil
The passage of the Dietary Supplement Health and Education Act (DSHEA) in 1994 amended the way in which dietary supplements for humans are regulated, but FDA concluded that DSHEA should not apply for animals.