Tag Archives: disease

Osteoporosis

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Osteoporosis is a disease that causes the density of bones to decrease. Normally bones are constantly being remodelled – some of the bone is broken down (resorped) and new bone grows in its place. In a normal person about ten percent of bone at any one time is undergoing this process. If there is a different in the rate of the two processes, with resorption occurring faster than growth, then osteoporosis will develop.

The two micrograph images below, from the Wellcome Collection, demonstrate the difference very clearly.

Normal Bone

Osteoporotic Bone

The holes in bones are required so that nutrients can get to the bones and also to give bones some “give” so that they are not too brittle; it’s important for bones to be able to bend a small amount to absorb shocks.

R0

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R0, also known as the basic reproduction number, is a measure of the ability of an infection to reproduce and spread in an unimmunised population. If R0 is less than one, each infected person infects (on average) less than one secondary person and the infection will die out. If R0 is greater than one then each infected person infects more than one secondary person and the infection will spread.

R0 varies greatly between diseases:

From the R0 figure the proportion of a population that must be immunised to prevent the spread of a disease can be calculated. If we use the population of the UK (61 838 154 according to 2009 figures from the World Bank) then we get the following graph:

You can see that for the most infectious disease on our list, measles, more than 93% (on average) of the population need to be immunised to prevent the disease from spreading (to prevent an epidemic). This is alarming in light of the failure of many parents to immunise their children due to unfounded fears about the MMR vaccine.

Lactose tolerance

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Because most in the western world are able to digest dairy products it is often assumed that this condition (lactose persistence) is the norm. But if you are able to tolerate lactose then you are actually in a minority: ninety-eight percent of Southeast Asians and ninety-five percent of Chinese are lactose intolerant. Between them these two ethnic groups make up more than 28% of the world’s population.

The graph below shows some of the ethnic groups with over 50% of the population lactose intolerant: