Determinants of Health

9. Biology and Genetic Endowment

Biology includes elements inside and outside our bodies. The internal influences include what is called a genetic endowment.

The biological determinants on the outside include all other living things that human beings encounter. Everything that lives – from a raccoon to a bedbug to a microorganism – is a biological determinant that can affect our health in both positive and negative ways. For example, exposure to harmful bacteria makes the human body use its built-in defence. This is when the immune system creates protective antibodies. A healthy immune system is in a better position to fight the bacteria off.

How our bodies are affected by these outside organisms can also be influenced by our genetic endowment.

Genetic endowment is what we physically inherit from our parents and ancestors. These family traits are visible in eye and skin colour, similar facial features and things like height.

A lot of other hereditary traits that cannot be seen are carried in DNA – the basic building block for all life. These traits determine blood group and metabolism, for example. They can also result in an increased risk of blood diseases, allergies, some cancers and many other diseases and health problems.

Women, biology and HIV

As noted elsewhere on this website, the risk of transmitting HIV from men to women is much higher than the other way around.

The vagina is particularly vulnerable to invasion by bacteria, viruses and other germs. It is an ideal place for bacteria to grow, as it is warm and moist. It also provides an easy entrance into the body … Women with low levels of the hormone estrogen may be at increased risk for transmission of HIV because low estrogen levels directly affect the vaginal wall, making it thinner so HIV can more easily pass through the wall.1

According to the Canadian AIDS Treatment Information Exchange (CATIE), not every woman shares the same level of biological risk.2 It can depend on her general health and the health of her genital tract. CATIE lists the common biological factors that can increase a woman’s sexual risk of

      HIV infection and explains them as follows:

    • Hormonal changes

While the role of the menstrual cycle and hormonal changes on the female genital tract is not clear, animal studies suggest that the lining of the vagina gets thinner closer to menstruation than during other parts of a woman’s cycle. This might mean that the risk of HIV infection could change with the cycle.

    • Vaginal flora (AVF) and bacterial vaginosis (BV)

The vagina is home to a lot of so-called friendly bacteria that make the female genital tract healthier. Changes in this bacteria can increase a woman’s risk of HIV infection by as much as 2.5 times. (Such change includes a decrease in good bacteria and an increase in bad bacteria.)

Having too much so-called bad bacteria is very common. It is easy to not even know there’s a problem. If there are any symptoms, they can include unusual discharge (fluid) from the vagina and a strong “fishy” or sour odour.

This is bacterial vaginosis – a bacterial infection.

    • Age

Young women seem to be much more vulnerable to HIV – especially when they are below 24 years of age. Their vaginas may be more likely to get tears and scrapes during sexual intercourse. Post-menopausal women also have a higher risk of HIV infection, because this is when the lining of the uterus gets thinner, and the vagina is drier.

    • Immature cervix (cervical ectopy)

Up until 18 years after birth, the cervix is still developing. In these years, the thinner cells that line the cervix are found further down into the vagina than they are in older women. This is called cervical ectopy or an immature cervix.

Because the cells lining the cervix offer a thinner and weaker barrier to HIV, young women with cervical ectopy have a much greater risk of HIV infection.

    • Pregnancy

Pregnant women could be more at risk because of increased hormones and changes to the immune system that are the body’s way of protecting a fetus.

 

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1Women and the Biology of HIV Transmission, online fact sheet, CATIE, as of June 2011
2IBID