The Season You Were Conceived Could Affect How Much 'Good' Fat You Have in Your Body, Study Suggests

Would-be fathers exposed to cold temperatures before they conceive could produce children with more active levels of "healthy" brown fat, according to research.

As existing evidence suggests environmental factors can affect how the genes of a sperm are expressed, researchers behind the study wanted to investigate whether the climate a baby is conceived in changes their body.

Their work hones in on brown adipose tissue, or brown fat, as opposed to white fat. The latter collects around the belly, and is used to store energy. In contrast, brown fat is used to keep us warm and gathers around the neck, torso, and in white fat reserves. Existing scientific evidence suggests brown fat burns a relatively large amount of energy when it is activated. It is believed the presence of it in the body could make it easier to lose weight, in the right conditions. It is also linked to a lower risk of becoming overweight or developing metabolic disorders, the authors noted.

"The study identifies for the first time a link between environmental temperature and offspring metabolism which is transmitted through the sperm," Dr. Christian Wolfrum, lead author of the study and associate professor of the Institute of Food Nutrition and Health at the ETH Zurich University in Switzerland, told Newsweek.

The team studied brown fat in mice and humans, and concluded males who are exposed to low temperatures before mating appear to produce offspring whose brown adipose tissue is more active.

In one part of the study, researchers looked at cross-section X-ray images of the bodies of 8,400 adults. They found that those born between July and November, and therefore conceived in the cooler months of the year, had significantly more active brown adipose tissue than those born between January and June, or conceived in the hotter portion of the year.

To further probe this apparent link, the researchers kept mice in either a moderate temperature of 23 degrees Centigrade (73.4 degrees Fahrenheit) or a cool 8 degrees Centigrade (46.4 degrees Fahrenheit) several days before they were allowed to mate.

Similarly to the human study, the offspring of the male mice kept in cool temperatures had more active brown adipose tissue compared with those of males kept in the moderate environment. What's more, when the mice were fed a high-fat diet, the offspring of cold mice gained less fat.

Meanwhile, the temperature the female mice were kept in appeared to make no difference to brown fat activity.

The team also studied sperm and in vitro fertilization, and found a father's ambient temperature affected how the genes of his sperm are expressed, or its epigenetics.

"Cold exposure of the father before conception leads to the development of more brown fat in the offspring, which in turn burns more energy and thus protects from the development of obesity," said Wolfrum.

The findings were published in the journal Nature Medicine, and mirrors previous research which suggests individuals from cold regions have high levels of brown fat.

However, Wolfrum acknowledged: "The data on the mechanism is derived from mice since it is impossible to study this phenomenon in humans.

"The human relevance is inferred from a retrospective study with approximately 9,000 people which showed that people conceived in colder month were more likely to have large amounts of brown fat. The problem is that there are many other parameters which could affect brown fat which cannot be controlled in such a study."

Temperatures could therefore play a role in the obesity crisis, suggested Wolfrum, as average temperatures indoors in the U.S. have risen in the past few decades. Previous research has indicated a person's home temperature is associated with their weight.

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"Maybe it would make sense to lower temperature in homes (especially in winter). From a molecular point of view we found multiple genes which might be used as targets for a pharmaceutical intervention," he said.

Next, the researchers will investigate the differences between the epigenetic programming of human sperm in the winter and summer.

So, should couples hoping to conceive taken a cold shower before trying to conceive in order to give their children a head start in being a healthy weight? Not quite, Wolfrum said in a statement.

"Before we can give that kind of advice, we need to study the correlation in people more closely. But it is likely that the exposure to cold needs to persist over a longer period for it to have an effect on epigenetic programming." Taking a dip in cold water or lying on a block of ice "probably won't be enough," he said.