It is August 14th and I am looking at this morning's headline in the Globe and Mail--"Invisible scientist, geriatric astronauts in dead heat." One can only pity future historians assigned to deciphering the hieroglyphics of our era! The headline refers, of course, to the big blockbuster hit of the summer, Space Cowboys. This movie is being described in the media as a "Geriatric NASA adventure". Beat that!
Well, two writers in the National Post tried to do just that. Playing on the public's insatiable interest in 'aging' male stars, the two writers, Botsford and Botsford-Fraser, put forward a movie premise that spoofs Space Cowboys. Their movie concept is titled, "Geriatric Superstar Chick Flick". Here is the concept: "four gorgeous, superstar, action hero, geriatric babe nuclear-sub experts reunite for a spectacular-underwater adventure." Although the premise might not appear sellable from the standpoint of a 'big' Hollywood producer, it is in step with the reality that a growing part of the population consists of "geriatric babes".
Not only are there more "geriatric babes" in society, but they are living longer and highlighting the difference in life span between men and women. Today, women in both developed and developing nations live approximately 7-10 years longer than men. This is not a statistical anomaly or a product of inequities in health care. On the contrary, men enjoy many physical and cultural advantages; for instance, men are typically stronger, faster and less overweight than women. They are generally wealthier, and have, historically, had better access to employment, education and health care. Studies show that men receive medical care more promptly for potentially lethal conditions. Also, until recently, many drugs have been approved on the basis of trials conducted predominantly on men. Should not all of these factors have given men a decided longevity advantage? Since the answer is no, what puts women so far ahead of the game? Although, we are only beginning to unravel the mysteries of aging, some research is beginning to emerge which sheds light on the gender discrepancy in life span.
Consider the following: The records of women outliving men date back to the earliest reliable church records or to the1500s.1 Back then, women lived an average of 36.6 years compared to 33.7 years for men. The female life span has increased by 77% since 1900, while the life span of men increased by only 66% during the same time period. Today, two-thirds of all people over the age of 65 are women. Among centenarians, 85% are women. Moreover, female centenarians as a group live several years longer than male centenarians.7
A phenomenon so universal should have it origins in evolution and genetics. Thomas Perls and Ruth Fretts of Harvard's Medical School, whose research focuses on this gender gap discrepancy, attribute the difference to the fact that "female longevity is more essential, from a Darwinian perspective, than the prolonged survival of males." Females are instrumental to the nurturing of offspring; consequently, this assures the passing of female genes to the next generation. By contrast, the critical factors for passing on male genes to the next generation is the practical necessity of safeguarding both the availability of males to females and the longevity of mothers, not the longevity of the males themselves.
If, indeed, female longevity is vital to the survival of the species, one should find multiple behavioral and physiological mechanisms that would reinforce this survival advantage. And indeed, recent research has revealed a number of interesting facts.
First, and perhaps most obvious, are the sex hormones. Testosterone has been found to be 'toxic' to the organism. Not only does testosterone promote aggressive and risky behaviour, potentially causing accidents and deaths, but it also increases levels of low-density lipoprotein, raising the male's chances of getting myocardial infarction and stroke. On the other hand, estrogen appears to be rather beneficial to the body. It lowers levels of low-density lipoprotein and raises levels of high-density lipoprotein by regulating the activity of liver enzymes involved in cholesterol metabolism. Estrogen also possesses antioxidant properties, thereby preventing DNA damage and cancer. Though this is still a subject of debate, studies indicate that estrogen administration after menopause lowers the risk of death from myocardial infarction and stroke and, importantly, the risk of dying in general.2,3 The trends connecting estrogen replacement therapy and longevity are, obviously, relatively recent and need to be confirmed in the future. What is clear is that one may want to think twice about taking testosterone for a boost later in life.
Another factor now thought to contribute to female longevity is menstruation. The regular bleeding, so often blamed for low blood and iron levels in pre-menopausal women, may actually contribute to longevity.4,5,6 Bleeding lowers the number of iron ions, essential to the formation of oxygen radicals, which, in turn, have been implicated in aging and cancer. Instead of being a defect, women's predisposition to light anemia may, in fact, be a mechanism for slowing down aging. Interestingly, a study performed at the University of Minnesota found that males who give frequent blood donations have a reduced oxidation of low-density cholesterol.
The 'last but not the least' explanation for the prolonged longevity of females may lie in the X-chromosome, which has been found to possess a gene crucial for DNA repair. Even though females undergo X-chromosome inactivation during adulthood and have only one active copy, similar to males, the inactivated X-chromosome seems to become more and more active with age. This 'shadow' activation can compensate in some fashion for the potential damage to the primary active X-chromosome in women. Men obviously do not have this advantage.
It would seem that there is a host of genes regulating senescence that could be targeted in an investigation of the genetic determinant of life span. Genes encoding sex hormones and genes controlling metabolism are good candidates. These genes are tuned to environmental and physiological cues that trigger repressor and effector mechanisms of senescence. Cues, such as reproduction and timing of reproduction, are the critical factors in the genetic nexus that controls these mechanisms. Since reproduction requires an enormous increase in resources, the body is intricately programmed to suppress reproduction until the time when sufficient resources are available. Delayed reproduction seems to repress senescence. Caloric restriction, with its demonstrated effect of slowing down aging, may in fact, be tied into this underlying mechanism, i.e., the body gets enough resources to maintain essential body systems but not enough to reproduce. In fact, starvation has been shown to suppress ovulation. This, of course, would indicate that women planning to conceive should not exercise caloric restriction. It would be interesting to find out whether this mechanism works in reverse: if one staves off having children, will certain life-extending mechanism be activated to ensure a sufficient time frame for rearing offspring later in life. Studies have shown that women centenarians are more likely to have given birth in their forties than women who died in their seventies. However, it is just a correlation and no causality has been established. With the introduction of the oral contraceptive, we have witnessed a startling increase in the age at which some women are having children. It remains to be seen what consequences this will have on the life span of the current generation or the next one.
In conclusion, it appears that while men are more 'fit to fight' in the short term, women are much more suited for longevity. However, living longer is not tantamount to being healthier. Statistically, women suffer from many more chronic conditions, such as osteoporosis. As well, men that pass over the so-called 'hump' (60-80 years) are in much better health than women of the same age. New scientific discoveries may find the means to confer the advantages of one sex on the other. In the meantime, you can look forward to next summer's blockbuster--it will have to be a "Geriatric Superstar Chick Flick".
E-mail your thoughts on this editorial and your casting line-up for the "Geriatric Chick Flick" to geriatrics@ribosome.com.
Suggested Reading
- Perls TT, Fretts RC. Why women live longer than men. Scientific American; June 1999.
- Liachenko A. HRT controversy unresolved until 2005. G&A; Jan/Feb 1999.
- Liachenko A. Pharmacological prevention of fractures. G&A; Nov/Dec 1998.
- Knekt P, Reunanen A, Takkunen H, Aromaa A, Heliövaara M, Hakulinen T. Body iron stores and risk of cancer. Int J Cancer 1994, 56(:3):379-82
- Gutteridge JM, Halliwell B. Free radicals and antioxidants in the year 2000. A historical look to the future. Ann N Y Acad Sci 2000, 899: 136-47
- Venarucci D, Venarucci V, Vallese A, Battilà L, Casado A, De la Torre R, Lopez Fernandez ME. Free radicals: important cause of pathologies refer to ageing. Panminerva Med 1999, 41(4): 335-9
- Statistics Canada http://www.statcan.ca/ Daily/English/990513/s990513c.htm.
