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Some high-dose nutritional supplements linked to ocular side effects
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The use of dietary supplements is extremely common, with one out of every five Americans taking at least one daily. However, while these supplements provide a variety of benefits, high doses may result in potentially dangerous ocular side effects. Practitioners should be aware of any ocular contraindications of supplements and question patients about their vitamin regimens.
Vitamins B2, B3, beta carotene
Vitamin B2 (riboflavin) is a water-soluble vitamin and a retinal photosensitizer, according to Stuart Richer, OD, PhD, FAAO, chief of the Department of Veterans Affairs Medical Center in North Chicago. For this reason, patients should avoid taking more than five times the recommended daily allowance. “However, no published studies are available,” Dr. Richer said in an interview with Primary Care Optometry News.
Vitamin B3 (niacin) has been known to cause a reversible toxic cystoid maculopathy, Dr. Richer said.
High-dose beta carotene has several known ocular side effects, including reversible discoloration of the skin, as well as an increased risk of lung cancer, said Dr. Richer. However, not all studies support this lung cancer risk, he said.
“It is best to take a moderate dose or a mixture of several carotenoids until more is known,” he said.
Calcium
Dr. Richer said the average U.S. diet already supplies about 700 mg of calcium per day. “With recommendations of an additional 1,200 mg to 1,500 mg from diet and supplements, many individuals, especially men, are being over-calcified through supplementation,” he said.
Systemically, this “over-calcification” is linked to kidney stones, mitral valve disease and calcification of small and large vessel vasculature.
“In addition, Bruch’s membrane and the ocular micro-vasculature become calcified,” Dr. Richer said. “The latter is a risk factor for age-related macular degeneration and, theoretically, other ocular-vascular disorders.”
Vitamin E
Overall, Dr. Richer said many practitioners are now recommending doses of 400 IU or less of natural alpha tocopherol (one of the eight isomers of vitamin E) due to the HOPE [Heart Outcomes Prevention Evaluation] trial.
“While this meta-analysis has been widely criticized, doses beyond 800 IU to 1,100 IU can theoretically result in blood thinning in susceptible individuals,” he said. “For general health maintenance, in patients without health challenges, the general dose now recommended is 200 IU of mixed natural tocopherol/tocotrienols (all eight isomers of vitamin E).”
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Platelet inhibitors
For patients who may be taking anti-coagulants, any compounds that inhibit clot formation can cause ocular side effects, according to Bruce E. Onofrey, OD, RPh, FAAO, a Primary Care Optometry News Editorial Board member and vice chair of eye care services at Lovelace Medical Center, Albuquerque, N.M.
“If a patient is taking Coumadin (warfarin, Bristol-Myers Squibb), it is not recommended that you give him or her flaxseed for dry eye; ginkgo, which is sometimes used for glaucoma or macular degeneration; vitamin E or fish oil,” Dr. Onofrey said in an interview. “Any of those compounds have the ability to inhibit platelets, especially when combined with aspirin. This is one cause of periocular hemorrhage or subconjunctival hemorrhage.”
Similarly, Dr. Onofrey said, patients on Coumadin should also not be given vitamin K compounds. “They inhibit the anticoagulant effect of Coumadin,” he said.
Other anticoagulant compounds that should not be combined with platelet-inhibiting supplements are heparin and Plavix (clopidogrel, Bristol-Myers Squibb/Sanofi), Dr. Onofrey said.
“Also, people who take NSAIDs regularly should avoid platelet-inhibiting supplements such as flaxseed oil, vitamin E, ginkgo and fish oil,” he said.
Dr. Onofrey added that the blood thinning risks of ginkgo are controversial. “While experimental evidence suggests that ginkgo has little or no effect on bleeding time or platelet activity, there are many cited cases of presumed cause and effect of increased bleeding from its use,” he said. “The clinician should be aware that this controversy exists and be skeptical, yet cautious, when evaluating patients that may present with signs of hemorrhage with a history of regular use of this nutraceutical compound.”
Dr. Richer also pointed out the potential dangers of fish oil in combination with anticoagulant drugs. “Be aware that higher doses may theoretically promote bleeding when used in combination with aspirin, high-dose vitamin E, Coumadin, ginkgo biloba, ginseng or other potential blood thinners,” he said. “However, documented cases are not to be found, and more rigorous recent multipatient studies are not drawing as much concern as previously conjectured. I would still be wary of combining high doses of multiple blood thinning pharmaceutical or nutraceutical agents in any given patient.”
Some evidence indicates that flaxseed should be avoided in patients with established malignant prostate cancer, he added.
“While some have discussed a possible increased risk of breast cancer with flaxseed use, I have found the opposite to be true,” said Dr. Onofrey. “Flaxseed is used by some women with breast cancer, and it is believed it may prevent metastatic cancer.”
Iron, ocular-vascular disease
For adults, particularly men, an increased consumption of iron can increase risk of cardiac disease, which is related to ocular-vascular disease, Dr. Richer said. “For every 1 mg of dietary iron, the risk of heart disease increases by 5%. So, for adults, iron should be acquired solely from the diet, not in a multivitamin, except under the care of a physician,” he said.
Exceptions to this rule are growing children and menstruating, pregnant or lactating women, he said.
Selenium, zinc
Low doses of selenium are considered useful in preventing cataracts, Dr. Richer said, but higher doses of this mineral have been found to actually induce a cataract.
For more information:
- Stuart Richer, OD, PhD, FAAO, is a distinguished practitioner, National Academy of Practices in Medicine. He can be reached at 3001 Green Bay Rd., North Chicago, IL 60064-3095; (224) 610-5440; e-mail: Stuart.Richer1@va.gov.
- Bruce E. Onofrey, OD, RPh, FAAO, can be reached at 5150 Journal Center Blvd NE, Albuquerque, NM 87109; (505) 275-4226; e-mail: Eyedoc3@aol.com.