Cataracts are a clouding of the eye's lens that commonly cause vision problems in older people. Some studies, but not all, have found that people with higher intakes of antioxidants, including vitamin C, may have a lower risk of developing the condition.

But those studies have been done in Western countries -- and not in lower-income countries like India, where people's vitamin C levels tend to be very low and rates of cataract are particularly high.

For the new study, researchers evaluated more than 5,600 Indian adults age 60 and up for cataracts. They also interviewed them about their diets and lifestyle habits, and measured their blood levels of vitamin C.

Overall, nearly 73 percent of the study participants were found to have cataracts. But that risk dipped as vitamin C blood levels and vitamin C intake rose.

In the roughly one-quarter of older adults with the highest vitamin C levels, the risk of cataract was 39 percent lower than in people with the lowest levels of the nutrient. That was with factors like income, smoking habits, high blood pressure and diabetes taken into account.

But vitamin C levels were generally very low. More than half of the study participants were deficient, and the bottom 30 percent of the group had vitamin C concentrations below the level of detection (2 micromoles per liter).

Anything below 11 micromoles per liter is considered a vitamin C deficiency.

Vitamin C is an antioxidant, which means it helps protect body cells from damage caused by so-called oxidative stress.