New Under the Sun:
Volume 3, Issue 6
This month we begin with a brief review of basic biology. What do we need to sustain life? Four of the basics are: breathable air, drinkable water, nutritious food, and plenty of sunshine. Although many science fiction authors portray human groups living underground, those authors ignore human biology and adaptations. As an intriguing thought puzzle, consider what resources would be necessary to maintain a population of 100 individuals, 50/50 male and female, underground for 20 years with no surface contact and no air exchange. What will their health status be after 20 years?
Why Women Live Longer: an adaptive explanation: A trip through any nursing home highlights the fact that women, on average, live longer than men. Higher male to female mortality rates are not just the case for humans, but are true throughout the animal kingdom. When scientists see a common pattern such as this, they search for adaptive/evolutionary explanations that work across a broad range of species rather than explanations that are species-specific. This section reviews an article by Kruger and Nesse who analyzed male:female death rates in several countries across a range of causes and put their results in an evolutionary perspective.
One of the cross-species explanations for the higher male mortality rate relates to sexual selection. That is, certain aspects of male behavior and appearance indicate higher quality to females. However, these same behaviors and traits can be costly to the male, increasing his probability of death. For instance, an animal with a large, muscular body, or a glossy coat, or bright plumage will generally be most attractive to females of its species because these are indicators of disease resistance and good health. However, they are costly traits to maintain in part because they require an optimal diet and other living conditions, and in part because they also lead to more intra-male competition for dominance. Males at the top of the hierarchy are far more reproductively successful than are males at the bottom, but it is also a strain on their health to maintain their position against rivals. The highest male:female differential in mortality occurs during young adulthood: exactly the period when males compete for mates.
“No guts, no glory” is a male mantra that leads to risk-taking behaviors of all sorts. It can also lead to reproductive success, so it is an attitude that has been selected for over time. A similar attitude among females would most probably result in reproductive failure due to death of their offspring. Therefore, as the authors put it, females have a “tend and befriend” response. Since investment in offspring is more costly for females than for males, it is more important for females to make sure their offspring survive than it is to fight for dominance; therefore, they work to strengthen social networks rather than to dominate them.
In modern societies, infectious diseases are no longer the primary causes of death. Among all causes of death, accidents rank fourth for men, but only seventh for women. Males commit suicide at far higher rates than do women. Men engage in more hazardous occupations than do women. And men are more likely to die from lung cancer and liver disease than are women.
Men are adapted to compete with other men for reproductive success, whether they consciously realize this or not. However, how that competition plays out and what effect it has on a male’s health and longevity can be modified culturally. If resources are limited, then competition may play out violently. If resources are more expansive, competition may be less violent, but no less fierce, when it is over extent of education and access to economic “goodies.” In the case of limited resources, the male mortality rate will continue to outstrip the female mortality rate (the exception being societies which practice purdah; see below). But when education and money are the competitive stakes, the gap between male and female mortality rates will lessen.
Analysis of mortality data in the US showed that for deaths before age 50, 16 men died for every 10 women, with the peak difference for those in their 20s. This held true for data from 20 other countries the authors analyzed. The issue for public health workers trying to reduce male mortality is this: how can risky behaviors be reduced if the socioeconomic environment is one of limited resources and few options? Kruger, DJ & Nesse, RM 2004 Sexual selection and the male:female mortality ratio. Evolutionary Psychology 2: 66-85.
Fish and Fetal Development: Intra-uterine growth retardation (IUGR) is associated with low birth weight and can lead to increased infant morbidity and mortality. Maternal diet can play a key role in whether or not IUGR is a problem during the third trimester. A British study analyzed whether there was an impact on birthweight when mothers ate fish during the last trimester. Fish are not only a good source of protein but, particularly for cold water fish, they are a good source of omega 3 fatty acids. These fats are involved in brain development. It has also been suggested that these fats may increase placental blood flow which would have the benefit of increasing fetal growth. Researchers in England questioned 11,511 women due to deliver between April 1991 and December 1992 about their third trimester fish consumption. Since oily fish have significantly more fatty acids, fish consumption was divided into categories of white fish, oily fish, and shellfish. Based on total fatty acid consumption, the women were divided into quintiles and the resulting answers were then compared to birth data. Confounding variables such as smoking, alcohol consumption, demographics, and maternal physical characteristics were taken into consideration. Women who took fish oil supplements were excluded from the study.
Analyses found no association between fish/fatty acid intake and the length of the pregnancy or tendency for preterm deliveries. However, there was a statistically significant negative association between fatty acid/fish intake and incidence of IUGR. That is, the more fish a woman ate in late pregnancy, the lower her probability of giving birth to an IUGR infant. Other studies have found that fish oil supplements can increase the incidence of IUGR. Therefore, it appears, as with studies on antioxidants, that one must actually eat a particular food to achieve a benefit. Taking supplements will not do the job and may even be counterproductive. Rogers I, Emmett P, Ness A, Golding J. Maternal fish intake in late pregnancy and the frequency of low birth weight and intrauterine growth retardation in a cohort of British infants. J Epidemiol Community Health. 2004 Jun;58(6):486-92.
Comment: I know regular readers of this newsletter are waiting for this so I will not disappoint. Here is yet another reason to eat sardines! If you cannot eat them straight out of the can, then try mixing them with avocado, tomato, olives, and spinach in a salad.
Bacteriophage Handcreams: Hospitals are a major source of staph infections, many of which have developed resistance to common antibiotics. Of particular concern is Staphylococcus aureus. New methods are needed to fight staph. One possibility that is being explored is the inclusion of phages in the hand washes and creams used in medical settings. In the past, it was thought that phages that destroy particular types of bacteria might be useful in fighting infections. However, maintaining large enough collections of the various phage types proved difficult, so that idea has been essentially abandoned. Nevertheless, phages may still have an important role to play. Researchers have shown that Phage K and modifications of that phage destroy a wide variety of staph types. When the Phage K mix was put in a hand wash and compared to regular hand wash, the amount of staphylococci was reduced 100 fold on the skin cleaned with the bacteriophage wash compared to that without. The bacteriophage achieves this result by invading and then destroying the bacteria cells. O'Flaherty S, Coffey A, Edwards R, Meaney W, Fitzgerald GF, Ross RP. Genome of staphylococcal phage K: a new lineage of Myoviridae infecting gram-positive bacteria with a low G+C content. J Bacteriol. 2004 May;186(9):2862-71.
Comment: Bacteriophage hand wash sounds like an excellent idea. However, it does require that medical personnel actually wash their hands frequently. As reported in a previous issue of this newsletter [Healthcare and Handwashing; January, 2004], one cannot assume that because a methodology is available that medical personnel will actually use it.
AnthroHealth Tip of the Month: Scare tactics to the contrary, humans require exposure to the sun (UVB radiation), especially during the summer, to maintain optimal health. The premier example of sun avoidance is a woman who wears a burqa and spends most of her daylight hours inside, a practice called purdah. A traditional Moslem woman should be the “poster child” for the dermatological community. The odds of her suffering from any form of skin cancer are exceptionally low. Unfortunately, the odds of her living a long, healthy life are also exceptionally low, in part due to the wearing of a burqa and the practice of purdah which work together to drastically limit the amount of vitamin D the woman can produce. This results in severe bone problems in both the woman and her offspring, who are also born severely vitamin D-deficient. Since vitamin D deficiency is also associated with a number of other health problems including some cancers, autoimmune diseases, and hypertension, among others, it is not too surprising that there are extremely high rates of maternal mortality among these women.
Humans need sunshine (UVB) exposure. We are adapted for it and will suffer negative health consequences without it. However, this does not mean that if some is good, more is better. Just as sitting near a campfire on a cool night is a good thing, but standing in the fire to get warmer is not too smart, exposing unprotected skin to the sun during the day is a good thing, but getting a sunburn is not. How much exposure is optimal? Well, that depends on where you live and how dark your skin color is. If you are very light and live in Arizona or south Florida, you probably only need 10 – 15 minutes exposure each day. If you are very dark and live in Seattle, you will probably not be able to get enough exposure. In that case, and for those who are concerned about sun exposure, you will need to take vitamin D supplements. Take cholecalciferol (D3) unbound to anything else such as calcium or vitamin A. The minimum dosage should be 1000 IU/day. If you are very dark and live in the north, the minimum dosage should probably be 2000 IU/day. Do not take more than 4000 IU/day. “Sunshine on my shoulders makes me happy.” Just don’t go for the burn.
© 2001-2009 Kathleen E. Fuller, PhD. All rights reserved.