WEDNESDAY, July 23 (HealthDay News) -- Eating half a serving of soy food a day lowers sperm concentrations and may play a role in male infertility, particularly in obese men, Harvard University researchers report.

The reason for this relationship between soy and sperm count isn't clear. However, researchers speculate that soy increases estrogen activity, which may have a negative affect on sperm production and also interfere with other hormonal signals.

"There have been a lot of interest in estrogen and isoflavones in particular and a potential relationship to fertility and other reproductive disorders," said lead researcher Dr. Jorge Chavarro, a research fellow in the department of nutrition at the Harvard School of Public Health.

Research in animals has shown that isoflavones and estrogen can have a potentially negative affect on reproduction, including decreased fertility, Chavarro said. However, there is very little evidence of how these findings apply to humans, he said.

The new research, he added, lends support to how results of animal studies apply to humans. But Chavarro considers the findings preliminary and inconclusive. "It's way too early to say stop eating soy foods," he said. "It's not time to worry about whether you're eating too much soy. There's not enough information to conclusively say that. "

His report was published in the July 24 online edition of the journal Human Reproduction.

For the study, Chavarro and colleagues collected data on 99 men who attended a fertility clinic for evaluation. The men were asked about how much of 15 soy-based foods they ate in the past three months.

The foods men were asked about included tofu, tempeh, tofu or soy sausages, bacon, burgers, soy milk, cheese, yogurt, ice cream and other soy products like roasted nuts and energy bars.

Because different foods have different levels of isoflavones, half a serving of soy is equal to about one cup of soy milk or one serving of tofu or soy burgers every other day, Chavarro noted.

Chavarro's team found that men who ate the most soy had 41 million fewer sperm per milliliter of semen compared with men who did not eat soy foods. Normal sperm counts range between 80 million and 120 million per milliliter, according to a press release from the journal, a monthly publication of the European Society for Human Reproduction and Embryology.

In addition, the researchers found that the link between soy and sperm concentration was stronger among overweight and obese men. Overweight and obese men produce more estrogen than thinner men, and soy may increase those estrogen levels even further, they speculated.

Moreover, the link between soy and sperm concentration was strongest in men with higher sperm concentrations. Men who have normal or high sperm counts may be more susceptible to soy foods than men with low sperm counts, Chavarro said.

Infertility expert Dr. Hossein Sadeghi-Nejad, an associate professor of urology at UMDNJ New Jersey Medical School and Hackensack University Medical Center, agreed that soy may be one factor affecting fertility, especially in overweight and obese men.

"When patients are overweight, the fat tissue converts male hormones to more female hormones," Sadeghi-Nejad said. "So, it is possible that the combination of this estrogenic source [soy] and the extra internal estrogen that is caused by the conversion of androgen to estrogen through the fat has a more deleterious effect in that group of patients."

In addition, Sadeghi-Nejad noted that although sperm counts decreased most among men who have the highest counts, that should not affect fertility, since sperm counts were still in the normal range.

"But this is a good reminder that if you have an overweight patient, with abnormal semen parameters, and a very high soy intake, it may be wise for them to decrease this factor," Sadeghi-Nejad said.

More information

For more about obesity and infertility, visit the Obesity Action Coalition   .

TUESDAY, July 8 (HealthDay News) -- An increasingly common therapy used for localized prostate cancer may not bestow any survival benefits on the patient beyond those seen with a simple "wait-and-see" approach.

Men taking androgen deprivation therapy, which shuts off male hormones that can promote tumor growth, even had a slightly lower prostate cancer-specific survival rate.

"This might give pause, and probably should give pause to people thinking about using this approach," said Dr. Robert Ennis, director of radiation oncology at St. Luke's Roosevelt and Continuum Cancer Centers in New York City. "There's always a gray area of patients. This might shift the balance."

But, Ennis added, "this is not an absolute, definitive, end-of-story type study." The research, which is in the July 9 issue of the Journal of the American Medical Association, only looked at whether patients lived or died. There may be other outcomes of this therapy that would make it worthwhile, Ennis said.

And androgen deprivation therapy has been shown to have a benefit in other scenarios, for example, when added to radiation therapy.

"This teaches us something about how we practice medicine, and it does give us reason for pause," said Dr. Otis Brawley, chief medical officer of the American Cancer Society. "A lot of doctors give androgen deprivation therapy without any evidence that it's a good thing for early-stage prostate cancer. One of the reasons we're in such a quagmire on prostate cancer is so many doctors have practiced medicine not supporting the clinical trials but just treating it the way they think they ought to be treating it."

"This is not the first research to show this. There are clinical trials out there that already suggest this is not beneficial, but people have done it anyway," Brawley added. There is also evidence that androgen deprivation therapy can increase the risk of diabetes, stroke and death, among other things. "While it can be useful in a small number, it [can be] quite harmful and should not be used arbitrarily."

Standard treatments for when prostate cancer is still confined to the prostate include surgery, radiation or "waiting and seeing."

"Prostate cancer is not as typical as some of other cancers. It grows at a slower pace, and it tends to occur in men that are elderly, so there a lot of other things going on like heart disease or lung disease or kidney disease or diabetes," explained study senior author Dr. Siu-Long Yao, a clinical assistant professor of medicine at the Cancer Institute of New Jersey in New Brunswick. "If you treat someone for prostate cancer, they could [still] drop dead from a heart attack. The key in this disease where it grows slower is prediction. Who's going to drop dead of a heart attack and who's going to have problems with prostate cancer. It leads to complexity. It's a guessing game more so than in other cancers."

Nowadays, however, more and more men, especially older men, are opting for primary androgen deprivation therapy (PADT) instead of the tried-and-true standards.

"A lot of men think surgery and radiation seem aggressive while observation seems like you're doing nothing," Yao said. "Men and their physicians have started looking for an alternative, which has become hormonal therapy. Use of [PADT] in this setting has grown tremendously in the last decade or two. It is the second most popular treatment [after surgery] but, in spite of that, nobody has really studied whether it works or not."

Yao and his colleagues looked at 19,271 Medicare patients aged 66 and over, none of whom had received "definitive local therapy" such as surgery.

Forty-one percent of the participants had received PADT for an average of 18 months; the rest had simply waited and watched.

There was no increase in 10-year overall survival rates among men taking PADT compared with men undergoing conservative management.

In fact, 19.9 percent of those taking PADT died of their prostate cancer within 10 years, compared with only 17.4 of those on the waiting approach.

A second study, this one presented at the European Society for Medical Oncology Lugano conference, found that the number of prostate tumor cells circulating in a patient's bloodstream can predict how effective the treatment is. On average, the fewer the circulating tumor cells, said researchers from the Royal Marsden NHS Foundation Trust in the United Kingdom, the longer the survival.

More information

Visit the National Cancer Institute for more on prostate cancer.