Vitamin A may not prevent asthma: study

By Genevra Pittman

NEW YORK | Thu Jul 14, 2011 5:43pm EDT

NEW YORK (Reuters Health) - Despite the important role of vitamin A in lung development, researchers have found that giving the nutrient to pregnant women or preschoolers in Nepal doesn't protect kids against asthma.

But the findings don't mean vitamin A isn't important, especially in regions where vitamin deficiencies are common, according to the scientists.

Women taking vitamin supplements had a lower chance of dying during pregnancy, for instance. And those who took vitamin A while pregnant had kids with larger lungs, which have been linked to better survival.

"We're kind of narrowing down what the effect of vitamin A is," said Dr. William Checkley, from Johns Hopkins University in Baltimore, who worked on the study.

The lungs need vitamin A as they are developing and the nutrient is also involved in keeping lung tissue healthy over time, the researchers explain in the European Respiratory Journal.

In addition, previous studies hinted that people with lower levels of vitamin A in their blood are more likely to have asthma. But those kinds of studies, called observational studies, can't tease out cause and effect. Checkley and his colleagues wanted to see if by adding vitamin A to kids' or pregnant women's diets, they might lower the children's risk of asthma.

So the team followed up on two different trials that gave vitamin A or vitamin-free placebo pills to Nepalese women or kids.

The studies involved more than 5,000 kids and young adults, age nine to 23, who had gotten vitamin A or a placebo as preschoolers, or whose mothers had done so before and during pregnancy. All of them were living in an area of rural Nepal where vitamin deficiency is common.

Researchers asked all the kids if they had problems with wheezing or coughing or had ever had asthma. They also tested how well the kids' lungs were working using a device called a spirometer.

Between zero and two percent of the kids said they had had asthma at some point, and less than one percent currently did so -- with no differences between the placebo and vitamin groups.

There were no differences in how many kids reported wheezing or coughing in the two groups either, or in how well their lungs worked.

Still, Checkley said the findings might have looked different in another location.

"The effect of vitamin A may vary as to the setting," he told Reuters Health. "The prevalence (of asthma) was low in Nepal."

In the U.S., for example, nearly 10 percent of kids are diagnosed with the disease.

It's possible that in an urban area where asthma is more common to begin with, giving pregnant moms or kids vitamin A may better protect kids against asthma, Checkley said.

It's also not clear how the findings would apply to a population where vitamin A deficiency wasn't such a problem.

More than 300 million people worldwide have asthma, Checkley said, and increases in asthma rates have put researchers on a search for possible culprits. Pollution and allergies have been linked to asthma, and food and nutrition are other targets of investigation.

"Obviously diet is still one of those questions -- is it important or not?" Checkley said. Researchers are still wondering, "Can we prevent or reduce the risk of asthma by giving (vitamin A) supplements?"

So far, his work suggests the answer is no -- at least in this group of kids, in one part of the world.

SOURCE: bit.ly/pHaFUy European Respiratory Journal, online June 23, 2011.

Vitamin C from food tied to lower cataract risk

1 of 2. Tomatoes are on display at an organic fruit and vegetable stall at a market in Montalivet, southwestern France, August 13, 2009.

Credit: Reuters/Regis Duvignau

By Amy Norton

NEW YORK | Thu Jul 14, 2011 2:41pm EDT

NEW YORK (Reuters Health) - Older adults who get very little vitamin C in their diets may have an increased risk of developing cataracts, a study in India finds.

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.

Even in the group with the highest vitamin C levels, the typical amount was just 38 micromoles per liter. By comparison, in cataract studies in Europe and the U.S., the "high-C" groups have had levels of 70 micromoles or higher.

The findings, reported in the journal Ophthalmology, do not prove that adequate vitamin C protects against cataracts.

But it's biologically plausible, said senior researcher Astrid E. Fletcher, a professor at the London School of Hygiene & Tropical Medicine in the UK.

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

"Laboratory and animal studies show vitamin C plays a very important part in defending the lens of the eye against oxidative stress," Fletcher explained in an email.

"The eye is particularly vulnerable to oxidative stress as the 'seeing' organ of the body," she added. "Light is essential for vision but light is also very damaging. The lens absorbs ultraviolet radiation, a major source of oxidative stress."

But that biological plausibility does not mean that older adults should load up on vitamin C supplements to ward off cataracts.

Fletcher said the current findings have relevance primarily for India, where people's vitamin C levels are generally low. They might also have implications for other lower-income countries, she added, but those studies have not been done yet.

In Western countries, studies have come to conflicting conclusions as to whether people with high vitamin C intakes have a lower cataract risk.

What's more, clinical trials that have tested high doses of vitamin C and other antioxidants for preventing cataracts have failed to show a benefit.

One reason, Fletcher noted, may be that well-nourished people in high-income countries already have fairly high vitamin C levels, and an extra dose from a pill has little benefit to offer. Vitamin C is water-soluble, and excess amounts are quickly excreted from the body.

Another possibility, according to Fletcher, is that taking a few nutrients in pill form simply does not mimic the effects of a good diet.

Foods high in vitamin C include citrus fruits like oranges and grapefruit, green and red peppers, kiwifruit, strawberries, broccoli and tomatoes. In the U.S., the official recommendation is for men to get 90 milligrams of vitamin C per day, while women should get 75 milligrams.

In this study, most older Indian adults were getting well below that.

If extra vitamin C was shown to lower cataract risk in India, the benefits could be substantial.

"India has the highest burden of blindness in the world," Fletcher said, "and the main cause is cataract."

SOURCE: bit.ly/pdR2l1 Ophthalmology, online June 27, 2011.

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