Why do women live longer?

“Men have a detrimental effect on lifespan,” The Daily Telegraph reported. The Times also covered the story, saying that research suggests that “genes that are passed on by fathers may be shortening the lifespans of their offspring”.

This study involved 13 genetically engineered mice that did not have any paternal DNA but had been engineered from egg cells from two female mice. On average, these mice had a longer lifespan than normal mice.

The question of why women live longer than men was not answered by this study. All humans inherit DNA from both parents. If the mother’s DNA increases lifespan, or the father’s DNA decreases it, this should equally apply to male and female children.

This is innovative research, but only in a small group of mice, which makes the results more likely to have occurred by chance. Also, the genetic modifications to the mice could be responsible for the differences in lifespan. In conclusion, the study has limited implications for understanding why women live longer than men.

Where did the story come from?

The research was carried out by Manabu Kawahara from Saga University and Tomohiro Kono from the Tokyo University of Agriculture in Japan. The study was supported by funding from the Grant-in-Aid for Research on Priority Area, and a Young Scientists grant from the Ministry of Education, Culture, Sports, Science and Technology of Japan. It was published in the peer-reviewed medical journal: Human Reproduction .

What kind of research was this?

This study in mice aimed to investigate why female mammals generally have a longer lifespan than males. In order to do this, the researchers used ‘bi-maternal’ mice, which do not have any paternal (male) DNA. These mice are created in the laboratory using egg cells from two female mice without the use of sperm.

What did the research involve?

The researchers engineered 13 bi-maternal mice by combining the DNA from adult mouse egg cells and egg cells taken from newborn mice (which had also been genetically engineered). Embryos that formed were then implanted into the uteruses of female mice.

The 13 bi-maternal mice were compared with 13 control female mice conceived through normal mating. Both groups of newborns were nursed by the control mothers. All mice were then fed a standard diet and kept in similar conditions. The lifespan of the mice was documented, and blood samples were taken.

What were the basic results?

On average, bi-maternal mice survived 186 days longer than controls (maximum lifespan 1,045 days compared with 996 days in the control mice). The blood tests showed that eight weeks after birth, these mice had a higher count of one of their white blood cells (eosinophils). The body weight of bi-maternal mice was also significantly reduced compared to the controls at 20 months of age.

How did the researchers interpret the results?

The researchers say that their findings demonstrate that DNA from the mother may play a role in the offspring’s longevity. They conclude that the findings imply that DNA from sperm has a detrimental effect on longevity in mammals.

Conclusion

This is innovative animal research, but it has limited implications for understanding why women live longer than men. All humans, both women and men, inherit DNA from both their parents. If DNA from the mother conferred an advantage to females, it should also apply to males.

Other limitations of the study include:

• Genetically engineered mice are clearly very different from humans. It is unclear how applicable these results are to humans.
• Factors other than the lack of paternal DNA could explain the findings, including major differences between the bi-maternal mice and the control mice. While the control mice’s DNA came from two fully-grown animals, half the bi-maternal mice’s DNA came from a newborn animal that had also been genetically engineered.
• Comparing only 13 bi-maternal mice with 13 normal mice is too small a sample on which to base any firm conclusions. Any differences in lifespan in such small numbers are very likely to have occurred by chance. Also, the lifespan of the mice indicates little about their health.
• The study was not investigating whether being raised by two mothers, or having no father figure, can affect lifespan – something that may be implied by the news headlines. Instead, the study only investigated the theoretical scenario of an animal receiving no male DNA.

The reason why women live longer than men has not been answered by this study. Genetics is only one factor that can affect lifespan. Medical illnesses, lifestyle, environment, and professional, social, and personal relationships (including child-parent) are all likely to have an impact.