Research updates
Osteoporosis   p 7
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4. What causes osteoporotic fractures? Link to the Medical Research Council web site
Graph of BMD change
Figure 10 The graph shows the change in bone mineral density (BMD) with age in women. After the age of 35 – 40 bone mineral density declines in both sexes but in women the loss accelerates after the menopause.
4.1 The risk factors
The disease becomes noticeable when an individual suffers an osteoporotic fracture. The risk of such a fracture is a combination of factors. They are:
  • risk of falling
  • bone mass density (BMD)
  • geometrical and architectural aspects of the bones.

Here we will be looking mainly at factors which determine bone mass density. You may like to look again at the graph showing BMD against age (Figure 10 - repeated from page 4) It tells us that the BMD of an individual in later life will depend two factors, which we will look at in the following sections:

  • the peak bone mass attained by early adulthood (section 4.2)
  • the subsequent rate of bone loss in later life (section 4.3).

Let’s look first at the determinants of peak bone mass.

4.2 Determinants of peak bone mass
The main determinants of peak bone mass are:
Let's look at these in more detail.


Age   years recommended daily
calcium intake (mg)
0 - 1 525
1 – 3 350
4 – 6 450
7 – 10 550
11 - 18 male 1000
11 - 18 female 800
19+ 700
lactation +500
Table 1. Recommended daily intake of calcium.


The most important nutrients for influencing peak bone mass are calcium and vitamin D.

Table 1 shows the calcium intake recommended by the Committee on the Medical Aspects of Food (COMA) to meet the needs of healthy people in various age groups. (Where individuals have, or are at risk of osteoporosis, this daily intake should be higher.)

Table 2 shows that dairy products are the best source of calcium (low fat varieties generally contain as much, if not more).

foodstuff calcium (mg)
food: 28 g cheddar cheese 202
carton of low fat yogurt 225
Mars Bar 90
packet of crisps 37
portion of chips 15
drinks: glass of whole milk 179
glass of semi-skimmed milk 183
glass of cola 6
Table 2. Amount of calcium in some common foodstuffs.

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Question 6 - Activity
Information about lifestyle factors and bone mass density was collected from 153 women, aged 21, living in the city of Bath. They were asked how long they spent walking outdoors on a typical day. The bone mass density (BMD) in the femoral neck (a region of the hip) in these women was measured. The data are summarised in a spread sheet (see below).

The data are grouped into five ranges of time spent walking. The values of the femoral neck BMD in g/cm2 are collected under each range.

Analyse the data and apply statistical tests to find:

  1. the mean value of the femoral neck BMD for each level of outdoor walking
  2. if there is a significant difference between the mean values of BMD at different levels of outdoor walking
  3. whether there is an association between the level of outdoor walking and the femoral neck BMD.
The spreadsheets

Click on the links below to download the spreadsheet as

In Microsoft Excel you can use the in-built functions to find averages of groups of data and their standard deviations. You can also use Excel to produce graphs.