ISLAMABAD - Contrary to popular belief that sunscreen protects bodies from overexposure and possibly from skin cancer, researchers are discovering that the product may not be so safe after all.

Cell toxicity studies by Dr Yinfa Ma, Curators’ Teaching Professor of chemistry at Missouri University of Science and Technology, and his graduate student Qingbo Yang, suggest that when exposed to sunlight, zinc oxide, a common ingredient in sunscreens, undergoes a chemical reaction that may release unstable molecules known as free radicals.

Free radicals seek to bond with other molecules, but in the process, they can damage cells or the DNA contained within those cells. This in turn could increase the risk of skin cancer.

Ma also found that the longer zinc oxide is exposed to sunlight, the greater the potential damage to human cells.

“Zinc oxide may generate free radicals when exposed to UV (ultraviolet) sunlight,” May said, “and those free radicals can kill cells.”

Ma studied how human lung cells immersed in a solution containing nano-particles of zinc oxide react when exposed to different types of light over numerous time frames.

Using a control group of cells that were not immersed in the zinc oxide solution, Ma compared the results of light exposure on the various groups of cells. He found that zinc oxide-exposed cells deteriorated more rapidly than those not immersed in the chemical compound.

Even when exposed to visible light only, the lung cells suspended in zinc oxide deteriorated. But for cells exposed to ultraviolet rays, Ma found that “cell viability decreases dramatically.”

When exposed to ultraviolet long-wave light (ultraviolet A or UVA) for 3 hours, half of the lung cells in the zinc oxide solution died. After 12 hours, 90 percent of the cells in that solution died, Ma found.

According to Ma, when the zinc oxide nano-particles in the solution absorb the UV rays, the reaction releases electrons, which in turn may produce unstable free radical molecules in the zinc oxide solution.

Those free radical molecules then bond with other molecules and act as parasites, damaging the other molecules in the process.

Ma’s research on zinc oxide’s effect on cells is still in the early stages, so he cautions people from drawing conclusions about the safety or dangers of sunscreen based on this preliminary research. “More extensive study is still needed,” Ma said. “This is just the first step.”

In the meantime, Ma advises sunbathers to use sunscreen and to limit their exposure to the sun. “I still would advise people to wear sunscreen,” he said. “Sunscreen is better than no protection at all,” Ma added.

Besides sunscreen, zinc oxide is used in many commercial products, including plastics, paints, ointments and sealants. The study will be published in the journal Toxicology and Applied Pharmacology.

BP drugs don’t reduce colorectal cancer risk

Contrary to current thinking, researchers of new study have found that taking beta-blockers that treat high blood pressure does not decrease a person’s risk of developing colorectal cancer.

The study also revealed that even long-term use or subtypes of beta-blockers showed no reduction of colorectal cancer risk. In recent years, researchers have thought that beta-blockers, which are prescribed to many older adults for high blood pressure and heart conditions, might be linked with a decreased risk of cancer.

This theory stems from animal and laboratory studies that found that the stress hormone norepinephrine could promote the growth and spread of cancer cells. Beta-blockers inhibit norepinephrine’s action, so it stands to reason that the medications could have anticancer properties. Previous studies on beta-blockers` effects on colorectal cancer risk have yielded inconsistent results.

To provide more thorough information, Michael Hoffmeister, PhD, of the German Cancer Research Centre, in Heidelberg, Germany, and his colleagues conducted personal interviews from 2003 to 2007 with 1,762 patients with colorectal cancer and 1,708 cancer-free individuals.

After taking into consideration certain patient characteristics (such as weight and smoking status) and other factors that might influence the results, the researchers found no link between beta-blocker use and colorectal cancer risk.

Previous studies had not taken these factors into consideration. Even when the investigators broke down their analyses by duration of use of beta-blockers, specific types of beta-blockers, active ingredients (metoprolol, bisoprolol, carvedilol, and atenolol), and sites within the colon or rectum where colorectal cancer developed, there was no link.

Overall, the results of this study do not support the hypothesis that using beta-blockers can lower one’s colorectal cancer risk.

 The findings also point to the importance of considering patient characteristics and other factors that might influence the results of studies that look at how medications affect patients`` cancer risk. 

The results have been published early online in CANCER, a peer-reviewed journal of the American Cancer Society.

Being born in winter may affect your mental health

The season in which a baby is born apparently influences the risk of developing mental disorders later in life; suggest researchers including one of Indian origin.

A large new study found a statistically significant peak of schizophrenia in individuals born in January.

The season of birth may affect everything from eyesight and eating habits to birth defects and personality later in life. Past research has also hinted the season one is born in might affect mental health, with scientists suggesting a number of reasons for this apparent effect.

“For example, maternal infections - a mother may be more likely to have the flu over the winter. Does this increase risk?” said researcher Sreeram Ramagopalan, an epidemiologist at Queen Mary University of London. “Or diet. Depending on the season, certain foods - fruits, vegetables - are more or less available, and this may impact on the developing baby.

“Or another key candidate is vitamin D, which is related to sunshine exposure. During the winter, with a lack of sunshine, mums tend to be very deficient in vitamin D,” Ramagopalan added.

However, this effect appears very small, and since past studies only looked at several thousand people at a time, there was a chance the link between birth month and later mental health might only be a statistical illusion.

Also, prior research often pooled data from different nations, complicating analysis, since population trends can vary substantially between countries.

To pin down whether or not there was a link between seasons and the mind, Ramagopalan and his colleagues analysed a very large number of births, all from the same country.

The scientists investigated whether the risk of schizophrenia, bipolar disorder and recurrent depression was influenced by month of birth in England.

This included nearly 58,000 patients with the disorders and more than 29 million people from the country’s general population. [10 Controversial Psychiatric Disorders]

The researchers found that all the mental disorders they looked at showed seasonal distributions. Schizophrenia and bipolar disorder had statistically significant peaks in January, and significant lows in July, August and September. Depression saw an almost significant May peak and a significant November deficit. “This result is further confirmation of seasonal variations in births of those later diagnosed with mental diseases,” said William Grant at the Sunlight, Nutrition and Health Research Centre at San Francisco, who did not take part in this research. “This implicates conditions during pregnancy. The two most likely factors are vitamin D status and temperature,” Grant noted.

Ramagopalan speculated that the differences in risk between the disorders could be a result of different factors, or the same factor being important at different periods of pregnancy.

For example, the same risk factor - say, vitamin D levels - could be important in the third trimester for schizophrenia and bipolar disorder and the second trimester for depression. “The major implication is that once we understand the cause of these effects, then we can intervene in terms of disease prevention,” Ramagopalan told Live Science.

Factors other than prenatal ones might be involved as well. For instance, children born late in the year may be relatively immature compared with older classmates, and thus do less well academically and socially, which might cause mental stress. “Further, we did not have details on socio-economic status or ethnicity, which may confound our results,” Ramagopalan said.

Future research to understand the causes of these effects “would require large birth cohort studies to follow individuals over time,” he added. The findings were reported last month in the journal PLoS ONE.