High doses of beta carotene supplements increase lung cancer risk

An animal study has shown that high doses of beta carotene supplements may increase the risk of precancerous changes in lung tissue. The changes were even more pronounced when the animals were exposed to cigarette smoke.

For six months, researchers at Tufts University in Boston fed ferrets either a normal diet or a diet supplemented with high doses (equivalent to 30 mg per day in an adult) of beta carotene. Some of the animals were exposed to high doses of cigarette smoke.

Examination showed that all of the ferrets receiving high dose supplements had precancerous lesions on lung tissue. This response seemed to be enhanced by exposure to tobacco smoke. Ferrets in the high dose group also had low levels of retinoic acid in their lungs, a form of vitamin A thought to protect against lung cancer.

Journal of the National Cancer Institute

Vitamin A linked to learning and memory

Results of a study published in the journal Neuron suggest that vitamin A affects cells in a region of the brain linked to learning and memory.

Researchers created special genetically altered mice, known as knockout mice, which were missing two brain-specific receptors for the vitamin. Although the mice developed normally, compared to ordinary mice they performed poorly on standard intelligence tests.

On further examination, the brain cells of the knockout mice were seen to lack the ability to undergo necessary changes in order to facilitate learning.

Neuron Online

Beta carotene may reduce risk of heart attack

Elderly people may be able to reduce their risk of heart attack by eating fruit and vegetables rich in beta carotene, according to Dutch researchers.

As part of The Rotterdam Study, the researchers followed the dietary and medical histories of 4802 people aged from 55 to 95 for four years. During this period 124 of the participants had heart attacks.

Analysis of the results showed that those with the highest daily intakes of beta carotene had a 45 per cent lower risk of heart attack, compared to people consuming the lowest amount of beta carotene. A combination of beta carotene from food and supplements led to a 50 per cent reduction in risk.

American Journal of Clinical Nutrition

Folate important for breastfeeding women

Vitally important in protecting against birth defects, adequate folate is also important for breastfeeding women.

Researchers from the University of Pennsylvania in the US enrolled 42 women in a double-blind, randomized trial. The women received a daily multivitamin and either a placebo or 1 mg of folic acid per day. At three and six months after birth the researchers measured folate stores in blood and breast milk, dietary folate concentrations and homocysteine levels. Infant measures of growth, milk intake, and folate intake were also assessed.

In the supplemented women, values at six months for folate stores, milk folate concentrations and plasma homocysteine were not significantly different from those at three months. Folate stores were higher in the supplemented women compared with unsupplemented women at six months. Folate levels in milk also declined in unsupplemented women and they had higher levels of homocysteine.

The researchers concluded that 380 mcg, the average folate intake of the women who did not take supplements was inadequate to meet the needs of breastfeeding.

American Journal of Clinical Nutrition

Tomatoes reduce the risk of cancer

Researchers analyzing the links between tomatoes and cancer risk have concluded that a high consumption decreases the risk.

The researchers, from Harvard Medical School and Brigham and Women's Hospital in Boston reviewed 72 studies and found that 57 of these showed a link between increased tomato intake and lower cancer risk. The results of 35 of these were considered to be statistically significant. Reduction in risk was usually around 40 per cent. None of the studies reported results that suggested that tomatoes increased the risk of cancer.

Many experts believe that the antioxidant, lycopene is the compound most likely to be linked to this reduction in risk.

Journal of the National Cancer Institute

Thiamin deficiency worsens symptoms of malaria

Thiamin deficiency seems to worsen the symptoms of malaria, according to researchers in the UK and Thailand.

The researchers compared the levels of thiamin in the blood of 77 patients with malaria with those of 50 people who had no trace of the malaria parasite in their blood.

The results showed that "12 of the 23 patients with severe malaria and 10 of the 54 patients with uncomplicated malaria tested positive for thiamin deficiency." None of the control patients had deficiency symptoms. Thiamin deficiency was especially pronounced in those who died from the disease.

The Lancet

Fiber may not protect against colon cancer

Results from the Nurses Health Study suggest that a high-fiber diet may not protect against colon cancer. This contrasts with several other studies that have shown reduced risk.

The study involved 88 757 women, who were 34 to 59 years old and had no history of cancer, inflammatory bowel disease or familial polyposis. The women completed a dietary questionnaire in 1980. During a 16-year follow-up period, 787 cases of colorectal cancer were documented. In addition, 1012 patients with adenomas of the distal colon and rectum were found among 27 530 participants who underwent endoscopy during the follow-up period.

After adjustment for age, established risk factors, and total energy intake, the researchers found no association between the intake of dietary fiber and the risk of colorectal cancer.

However, researchers emphasize that fiber does have clear health benefits. Plant fiber comes in several different types and it may be that some types are more protective than others.

New England Journal of Medicine