A regular diet of even modest amounts of food containing soy may halve sperm concentrations, suggest scientists.
The study, published in the journal Human Reproduction, found 41 million fewer sperm per millilitre of semen after just one portion every two days.
The authors said plant oestrogens in foods such as tofu, soy mince or milk may interfere with hormonal signals.
However, a UK expert stressed that most men in Asia eat more soy-based products with no fertility problems.
“Oestrogenic compounds in food or the environment have been of concern for a number of years, but we have mostly thought that it was boys exposed in the uterus before birth who were most at risk” says
Dr Allan Pacey,Sheffield University
Animal studies have suggested that large quantities of soy chemicals in food could affect fertility, but other studies looking at consumption in humans have had contradictory findings.
The men were divided into four groups depending on how much soy they ate, and when the sperm concentration of men eating the most soy was compared with those eating the least, there was a significant difference.
The “normal” sperm concentration for a man is between 80 and 120 million per millilitre, and the average of men who ate on average a portion of soy-based food every other day was 41 million fewer.
Dr Jorge Chavarro, who led the study, said that chemicals called isoflavones in the soy might be affecting sperm production.
These chemicals can have similar effects to the human hormone oestrogen.
Dr Chavarro noticed that overweight or obese men seemed even more prone to this effect, which may reflect the fact that higher levels of body fat can also lead to increased oestrogen production in men.
However, the study pointed out that soy consumption in many parts of Asia was significantly higher than even the maximum found in these volunteers.
Dr Allan Pacey, a senior lecturer in andrology from the University of Sheffield, said that if soy genuinely had a detrimental effect on sperm production, fertility might well be affected in those regions, and there was no evidence that this was the case.
“Many men are obviously worried about whether their lifestyle or diet could affect their fertility by lowering their sperm count.
“Oestrogenic compounds in food or the environment have been of concern for a number of years, but we have mostly thought that it was boys exposed in the uterus before birth who were most at risk.
“We will have to look at adult diet more closely, although the fact that such large parts of the world have soy food as a major part of their diet and don’t appear to suffer any greater infertility rates than those on western diets suggests that any effect is quite small.”
US researchers have discovered that Vitamin D protects not just against rickets, osteomalacia and osteoporosis but also against heart diseases, cancer, diabetes and other ailments.
CLICK & SEE
Medical researchers are homing in on a new wonder drug that can significantly reduce the risk of heart disease, cancer, diabetes and many other diseases — sunshine.
A recent study found that men who are deficient in the “sunshine vitamin”, vitamin D, have more than double the normal risk of suffering a heart attack. Another study last week found that low levels of vitamin D increase the risk of diabetes, and a study last month linked deficiencies to an increased risk of dying from breast cancer.
The new findings join a growing body of evidence indicating that an adequate level of the vitamin, which most people can get from 20 daily minutes in the sun, is crucial to maintaining good health.
Not every scientist agrees, and there is controversy about what should be considered an adequate level of vitamin D in the blood. But sentiment gradually is shifting toward a higher intake.
“We don’t have a cause-and-effect relationship here yet,” said biochemist Hector DeLuca of the University of Wisconsin, in the US, to prove that higher doses of vitamin D prevent these diseases. DeLuca was the first to demonstrate how the vitamin interacts with the endocrine system, which manages the body’s hormonal balance.
But the links are so suggestive “that we have to pay attention to keeping blood levels up where they will protect,” he said. Until the protective effect is proved, he added, “what’s wrong with keeping an adequate level of vitamin D in the blood in case it is?”
Until recently, vitamin D was viewed primarily as a protective agent against diseases of the bone, such as rickets, osteomalacia and osteoporosis. Recommendations for the vitamin are based on preventing these disorders and call for a relatively small intake — a minimum of 400 international units (IUs) per day and perhaps twice that for elderly people, who don’t get outdoors much.
The vitamin is produced from natural precursors in the body by exposing skin to ultraviolet B in sunlight. Caucasian sunbathers can get 20,000 IUs in 20 minutes at noon in summer. But any additional exposure simply damages the skin.
Darker skinned people need three to five times the exposure to produce the same amount. Sunblock interferes with production by screening out ultraviolet light.
The primary sources of vitamin D in the diet are milk, which is fortified to yield about 100 IUs per glass, and oily fishes, which have a high content. To have an adequate intake, most people must take supplements or spend more time in the sun — a recommendation that dermatologists generally oppose because of the risk of skin cancer.
Current guidelines call for blood levels of about 30 nanograms per millilitre. By that definition, perhaps 10 per cent to 15 per cent of the white US population and 50 per cent of the black population is deficient in summer, with levels rising in winter when there is less sunlight.
Many researchers now say we should be striving for average blood levels of 50 to 60 nanograms per millilitre, at which level the bulk of the US population would be considered deficient.
Most researchers in the field take supplements of at least 1,500 IUs per day. Most recommend taking no more than 4,000 IUs because of potential toxicity.
Experts attribute the vitamin D deficiency, in part, to modern lifestyles. Video games and computers have brought children indoors, minimising their exposure to sunlight. Fear of cancer and increasing use of sunblock also might have contributed.
In the new analysis, Dr Edward Giovannucci of the Harvard School of Public Health and his colleagues studied 18,225 men enrolled in the Health Professionals Follow-Up study, a subgroup of a much larger ongoing study. The men submitted blood samples when they enrolled in the study, mostly in 1993 to 1995, and the samples were stored.
In 10 years of follow up, the team identified 454 men who had a nonfatal or fatal heart attack. They matched these men with about 900 other study members who did not have an attack, then measured vitamin D levels at study entry.
They reported in the current issue of the Archives of Internal Medicine that men with blood levels below 15 nanograms per millilitre had two and a half times the risk of having an attack or dying. When they controlled for all other possible factors, such as hypertension, obesity and high lipid levels, the risk was still twice as high as it was for the controls.
Men with levels between 15 and 29 nanograms per millilitre also had an increased risk. Unfortunately, Giovannucci said, there were not enough men in the group with levels above 35 nanograms per millilitre to determine whether higher levels are more protective.
The findings are “not out of left field”, he said. Many epidemiological studies have found a lower rate of heart attacks at higher latitudes, at lower altitudes and in winter — all of which correlates to decreased exposure to sunshine.
“They certainly have made the link between diabetes and cardiovascular disease,” said Dr Mason Weiss, a cardiologist at Centinela Hospital Medical Centre in Inglewood, California, who was not involved in the study. “Now the research must be on what the mechanism is.”
Giovannucci speculated that several mechanisms could be responsible for the observation. Previous studies have suggested that low vitamin D levels lead to a build-up of calcium in atherosclerotic plaques on the walls of arteries, increasing the risk of heart attacks.
It also could affect blood pressure or the functioning of heart muscles, making them more susceptible to arrhythmia.
“We obviously need to understand the mechanism better,” Giovannucci said. “But that requires randomised trials, which is a big undertaking.”
Weiss joined the chorus of researchers calling for changes in federal guidelines to reflect the new data.
“The next time they review the daily requirements, they should look at all these articles,” he said. Increasing the recommended intake of vitamin D “could have a significant health benefit,” he said, and would be a very cost-effective change.
Women who consume alcohol moderately on a daily basis are about 20% less likely than abstainers to experience poor memory and decreased thinking abilities, according to recent research. The senior author of the study explains that â€œWomen who consistently were drinking about one-half to one drink per day had both less cognitive impairment as well as less decline in their cognitive function compared to women who didn’t drink at all.â€
Researchers at Harvard School of Public Health and Brigham and Women’s Hospital analyzed data from 12,480 women age 70 to 81 who participated in the Nurses’ Health Study beginning in 1980.The study was twice as large as any earlier study and also investigated the effects of different forms of alcohol on cognition and memory.
It didnâ€™t matter whether the women drank beer, wine, or liquor (distilled spirits). The positive effects of the alcoholic beverages were all the same.
Although the study only examined women, previous research indicates that men benefit from substantially higher levels of alcohol consumption – one to two drinks each day.
There have been more than sixty prospective studies from around the world, which suggest that men and women who drink alcohol moderately have a lower risk of coronary heart disease,diabetes, and overall mortality.Data suggest that this benefit is independent of other diet or lifestyle factors which may be related to moderate alcohol consumption.Sound evidences are there that the benefits are attributable to a higher HDL cholesterol level and a slower blood clotting time among the moderate drinkers.