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Safety of Garlic, Lutein and Evening Primrose Oil Dietary Supplements

[Grazing horse]

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:

Lutein

  • For horses, the PSI is 8.3 mg/kg BW when obtained from forage or natural sources; no data exist to support recommendations regarding supplements.
  • For dogs, the PSI is 1.8 mg/kg BW, with an HSI of 0.45 mg/kg BW.
  • For cats, the PSI is 7.2 mg/kg BW, with an HSI of 0.85 mg/kg BW.

Evening Primrose Oil

  • For horses, the PSI is 400 mg/kg BW, which assumes the intake of total fat will not exceed 23 percent of the diet, including any quantity of evening primrose oil added.
  • For dogs, the PSI is 424 mg/kg BW, which is the upper level used in clinical trials.  Most likely the upper safe intake is higher than this.
  • For cats, the PSI is 391 mg/kg BW.  It is also likely that cats could tolerate higher levels.
    • Garlic

      • For horses, the PSI is 90 mg/kg BW, with an HSI of 15 mg/kg BW.  
      • For dogs, the PSI is 56 mg/kg BW; garlic has a long history of safe use as a supplement, with mean levels of 22 mg/kg BW being reported without serious adverse events.  
      • For cats, there are insufficient data to support a generic recommendation that covers all garlic preparation types, and the committee was not able to establish a PSI of garlic for cats.  However, mean intake levels of 17 mg/kg BW have been reported with apparently no serious adverse events.

      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. 

      References
      1. Dietary Supplements For Horses, Dogs And Cats Need Better Regulation, New Report Says (sciencedaily.com)
      2. Lutein and Zeaxanthin and Their Potential Roles in Disease Prevention 'Judy D. Ribaya-Mercado, ScD and Jeffrey B. Blumberg, PhD, FACN. In: Journal of the American College of Nutrition, Vol. 23, No. 90006, 567S-587S (2004)
      3. Supplement: Significance of Garlic and Its Constituents in Cancer and Cardiovascular Disease. Clarifying the Real Bioactive Constituents of Garlic. Harunobu Amagase. In: American Society for Nutrition J. Nutr. 136:716S-725S, March 2006
      4. Aged Garlic Extract, a Modulator of Cardiovascular Risk Factors: A Dose-Finding Study on the Effects of AGE on Platelet Functions. M. Steiner2 and W. L. In: 2001 The American Society for Nutritional Sciences
      5. A comparison of evening primrose oil and sunflower oil for the management of papulocrustous dermatitis in cats. Harvey RG. In: Vet Rec. 1993 Dec 4;133(23):571-3

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