Two studies published just a few months apart have revealed that taking certain antidepressants or hormone replacement therapy (HRT)-drugs used by millions of people worldwide-can dramatically increase the risk of cataracts.
The antidepressant study-the first major investigation into such a possible link-analyzed data from nearly 19,000 elderly cataract patients and around 190,000 controls. It found that those currently taking selective serotonin reuptake inhibitors (SSRIs), the most widely pres-cribed antidepressants in many countries, were 15 per cent more likely to have cataracts. In the US alone, this means that 22,000 cataract cases may be due to SSRI use.
The association was especially strong for Paxil (paroxetine), Effexor (venlafaxine) and Luvox (fluvoxamine). Paxil increased cataract risk by 23 per cent, Effexor by 33 per cent and Luvox by a whopping 39 per cent. Happily, the higher risk was linked only to current drug use (Ophthalmology, 2010; 117: 1251-5).
Although more research is needed to confirm the link, previous animal studies have suggested a plausible explanation for the increased risk of cataracts among SSRI users.
"The eye's lens has serotonin receptors, and animal studies have shown that serotonin can make the lens opaque and lead to cataract formation," said study author Dr Mahyar Etminan. "If our findings are confirmed in future studies, doctors and patients should consider cataract risk when prescribing some SSRIs for seniors," he added.
The other study linking cataracts to prescription drug use was an eight-year investigation of more than 30,000 postmeno-pausal Swedish women, which found that those using or who had used HRT had significantly higher rates of cataract removal than those who had never used HRT. Indeed, cataract removal risk was increased by 14 per cent in women who had ever used HRT and by 18 per cent in current HRT users-and the longer a woman used HRT, the higher was her risk.
Alcohol consumption also appeared to increase harmful HRT effects. Current HRT users who also reported having more than one alcoholic drink per day had a 42-per-cent greater risk of having to undergo cataract removal compared with women who used neither HRT nor alcohol (Ophthalmology, 2010; 117: 424-30).
As a plausible mechanism for how HRT could cause cataracts, it may be that HRT increases levels of C-reactive protein, high levels of which have been associated with cataracts in other studies.
As lead author Dr Birgitta Lindblad said, "If future studies confirm the associations we found, increased risk for cataract removal should be added to the list of potential negative HRT outcomes."
These new findings suggest that, in many cases, cataracts could be prevented by avoiding certain drugs. But it's not only SSRIs and HRT that have been linked to cataracts. Other studies have found significantly increased risks with statins (BMJ, 2010; 340: c2197), oral and inhaled cortico-steroids (Ophthalmology, 2009; 116: 652-7), antidiabetes drugs (Ophthal-mology, 2001; 108: 1670-4) and some sun-sensitizing medications, such as the painkilling non-steroidal anti-inflammatory drug (NSAID) naproxen (Arch Ophthalmol, 2010; 128: 959-63).
The importance of diet
On the other hand, researchers are also finding that a healthy diet can offer powerful protection against cataracts. Scientists from the University of Wisconsin's Department of Ophthalmology and Visual Sciences found that women who ate foods rich in vitamins and minerals were less likely to develop nuclear cata-racts-those forming in the centre of the lens-the most common type of cataract.
The study involved over 1800 women, aged between 55 and 86 years, who took part in the Carotenoids in Age-Related Eye Disease Study (CAREDS). The daily diets of these women were assessed according to their responses to a food-frequency questionnaire (the 1995 Healthy Eating Index, HEI), while the presence of nuclear cataracts was determined four to seven years later. These women's diets were also assessed to see how closely they reflected the 1990 dietary guidelines for Americans.
A high HEI score was the strongest modifiable predictor of a low prevalence of nuclear cata-racts. What contributed to the higher healthy diet scores were intakes at or above the recom-mended levels for vegetables, fruits, grains, milk and meat (or beans, fish or eggs), and below-recommended levels of fat, saturated fat, cholesterol and salt. Women with the highest HEI scores were found to have a 37-per-cent lower risk of developing cataracts than those with the lowest scores.
"These data add to the body of evidence suggesting that eating foods rich in a variety of vitamins and minerals may contribute to postponing the occurrence of the most common type of cataract in the United States," the research-ers concluded (Arch Ophthalmol, 2010; 128: 738-49).
There's also evidence to suggest that specific nutrients might be especially helpful for warding off cataracts. In an earlier study by the same team of researchers from the University of Wisconsin, women with high dietary intakes of lutein and zeaxanthin-found in dark green leafy vegetables, as well as in kiwi fruit, grapes, corn and egg yolk-had a 23-per-cent reduced preva-lence of nuclear cataracts. Those with the highest intakes of these nutrients were 32-per-cent less likely to have nuclear cataracts compared with those who had the lowest intakes.
The researchers also comment-ed that lutein and zeaxanthin, both of which accumulate in the lens of the eye, are known to protect against photodamage (caused by ultraviolet radiation), which predisposes to cataracts (Arch Ophthalmol, 2008; 126: 354-64).
A number of other nutrients, mostly antioxidants, also appear to be important for cataract prevention. A 10-year study of more than 2400 older adults in Sydney, Australia, found that higher intakes of vitamin C (from both food and supplements) or the combined intake of multiple antioxidants (vitamins C and E, beta-carotene and zinc) signifi-cantly reduced cataract risk (Am J Clin Nutr, 2008; 87: 1899-905).
Oxidative stress is thought to play a significant role in cataract formation, so it makes sense that antioxidants-which mop up free radicals that damage proteins and fibre cells in the lens-can be protective. Indeed, a study in North India showed that having higher levels of antioxidants in the blood-including vitamin C, alpha-/beta-carotene, zeaxanthin, lutein and lycopene-led to a significantly lower likelihood of having cataracts (Invest Ophthalmol Vis Sci, 2008; 49: 3328-35).
Reducing the risk
Besides avoiding certain drugs and eating a healthy, antioxidant-rich diet, there are a number of other ways to reduce your risk of cataracts.
u Stop smoking. Smokers are more likely to have cataracts, so kicking the habit may help to save your sight (Arch Ophthalmol, 1997; 115: 1296-303). It's thought that the cadmium in cigarettes accumulates in the lens and causes damage. Also, cigarette smoke is rich
in free radicals, among other things, so it could also be that smoking depletes levels of protective antioxidants (Br J Ophthalmol, 1998; 82: 186-8).
u Lose weight. Researchers at Harvard University found that people with a body mass index (BMI) of 30 kg/m2 or more (obesity) increased their risk of cataract by at least a third compared with a BMI of 23 kg/ m2 (overweight) or less (nor-mal) (Int J Obes Relat Metab Disord, 2002; 26: 1588-95).
u Drink in moderation. The 10-year Blue Mountains Eye Study in Australia (described above) found that people who drank more than two standard alcoholic drinks per day or were total abstainers were significantly more likely to undergo cataract surgery compared with moderate drinkers. Indeed, in this study, a moderate consumption of alcohol-one or two drinks a day-was associated with a 50-per-cent lower incidence of cataract surgery (Am J Ophthal-mol, 2010; 150: 434-40).
u Exercise. A recent study has reported that vigorous exercise can protect against cataracts. The researchers found that men who ran 64 km/week or more had a 35-per-cent lower risk of developing cataracts compared with men who ran less than 16 km/week.
Using these men's perfor-mances in 10-km races, which provide a good measure of overall and cardiorespiratory fitness, it was also found that the fittest men had only half the cataract risk of those who were the least fit (Invest Ophthalmol Vis Sci, 2009; 50: 95-100).
u Minimize heavy-metal expo-sure. Long-term, low-level exposure to toxic metals-and lead, in particular-results in their accumulation in the lens. Such a buildup increases the oxidative burden of the lens, thus leading to cataracts (JAMA, 2004; 292: 2750-4).
u Sport those sunglasses. When Japanese researchers reviewed studies carried out in Japan as well as in Iceland, Australia and Singapore, they found that those exposed to the highest levels of sunlight (ultraviolet light) also had the highest incidences of cataracts (Invest Ophthalmol Vis Sci, 2003; 44: 4210-4).
For more information on cataracts, consult the WDDTY Good Sight Guide.
Factfile: Promising natural treatments
u Bilberry is rich in anthocyanosides, potent antioxidants with a particular affinity for the eyes. In a report of 50 patients with senile cataracts, a combination of bilberry
(180 mg twice daily)-standardized to 25-per-cent anthocyanosides-and vitamin E (100 mg twice daily) for four months stopped the progression of cataracts in 96 per cent of the treated patients compared with 76 per cent of the control group (Altern Med Rev, 2001; 6: 141-66).
u Vitamin E was also tested on its own in a randomized controlled trial (RCT) of 50 patients with senile cataracts
(100 mg twice daily for 30 days). Compared with a placebo, there was a significantly smaller increase in the size of cortical cataracts (those in the outer rim of the lens) in the vitamin E group (Ann Nutr Metab, 1999; 43: 286-9).
u N-acetylcarnosine-containing eye drops called Can-C have shown potential in the treatment of cataracts. An RCT of 49 patients reported that, after six months of twice-daily Can-C use, 90 per cent of the NAC-treated eyes improved in visual acuity and 89 per cent improved in glare sensitivity. The overall visual outcome in the control group showed significant worsening after two years. It should be noted, however, that this study was conducted by the company-Innovative Vision Products (IVP)-that helped to develop the eye drops (Drugs R D, 2002; 3: 87-103).
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