Importance of body weight and bone size on bone mass

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Hi All, the PDF-available below paper may seem at first fairly obvious, but

the paper had some surprises for me.

The lower-weight women ate the same number of calories and exercised less?

Like CRONers, their body mass index average below 19.

Body fat was 10% lower, similar to CRON women, I believe.

Their diet compositions were highly similar.

Cheers, Al.

Rollins D, Imrhan V, Czajka-Narins DM, Nichols DL.

Lower bone mass detected at femoral neck and lumbar spine in lower-weight

vs

normal-weight small-boned women.

J Am Diet Assoc. 2003 Jun;103(6):742-4.

PMID: 12778047 [PubMed - in process]

Sixty-one nonsmoking, healthy, young, menstruating women

aged 18 to 30 years generally considered at peak skeletal bone mass

were screened for diseases and drugs known to adversely affect

bone mineral density (BMD). Anthropometric measures, BMD of the

lumbar spine (LS) and femoral neck (FN), exercise time, selected

nutrient, and energy intake were compared. The women were

categorized by frame size and body mass index (BMI), with

the upper range for normal weight (NW) being BMI 23.0 to 25.9 (n=30)

and lower weight (LW) being BMI 16.0-19.9 (n=31). Multivariate

t tests, Pearson correlations, and independent sample t tests were

used for statistical analysis. Ten of 21 in the LW group, all with

small frames, had varying degrees of low BMD of the LS and/or FN.

The amount of exercise time was greater in the NW group. Energy

and nutrient intakes did not differ significantly between groups. J

Am Diet Assoc. 2003;103:742-744.

……………..

Methods

…………………..

Each participant was asked to estimate the amount of time in

minutes per week that she currently participated in some type of

exercise or physical activity, including walking, running, biking,

swimming, aerobics, dance, calisthenics, weight training, or other

type of activity. She was also asked about her involvement in

physical activity or athletics during childhood and high school,

including gymnastics, dance, cheerleading, and sports.

All participants were given instructions for completing a self-

report, 5-day food intake record at home the week prior to their

scheduled bone scan. Each record was reviewed with the

participant to verify accurate inclusion of type and amount of food,

beverage, and supplement intake for 3 weekdays and 2

weekend days. Nutrient intakes were estimated using the Windows-based

Nutrition Data System for Research (NDS-R) software version

4.01 (1998), developed by the Nutrition Coordinating Center (NCC) at

the University of Minnesota.

Results

There were no statistical differences between groups for age, height,

or gynecologic age (years from menarche to current age). Body

weight, BMI, and percentage body fat were significantly different

between the groups (Table 1).

Table 1. Demographic and anthropometric characteristics for

normal-weight and lighter-weight participants

Normal weight (N=30)

Lighter weight (N=31)

Mean+/-SDa

Age (y)

23.7+/-3.5

24.3+/-3.3

Height (in)

64.7+/-2.6

65.3+/-2.6

Weight (lb)*

146.1+/-12.2

114.8+/-11.5

BMI (kg/m2)*

24.6+/-.9

18.9+/-1.0

% Body fat*

34+/-4

24+/-5

Gynecologic age (y)b

10.5+/-4.1

10.8+/-3.5

Physical activity (min/wk)**

261+/-259

148+/-154

Kcal in diet

1,869+/-487

1,830+/-407

Calcium in diet (mg)

1,002+/-370

973+/-414

Carbohydrate in diet (g)

246+/-58

238+/-60

Protein in diet (g)

71+/-18

69+/-17

Fat in diet (g)

68+/-28

68+/-22

Fiber (g)

17+/-6

15+/-7

a SD=standard deviation.

b Gynecologic age is the number of years since the first menses.

* Results significant at P<.01 using independent sample t test.

** Results significant at P<.05 using independent sample t test.

In the NW group, body weight was significantly correlated to the

femoral neck BMD (r=0.380; P<.05), and BMI was significantly

correlated to the lumbar spine BMD (r=0.468; P<.01). No such

correlation existed in the LW group. Body frame size estimations

indicated that more participants were considered to have a small

frame size in the LW group and medium or large frame sizes in the

NW group (Table 2).

Table 2. Mean bone mineral density and T scores for lumbar

spine and femoral neck for normal-weight and

lower-weight participants by frame size within each group

Normal weight (N=30) Sa=5, Mb=14, Lc=11

Lighter weight

(N=31) Sa=21, Mb=8, Lc=2

Mean BMD

lumbar

spine

(g/cm2)

Mean T

score lumbar

spine

Mean BMD

femoral

neck (g/cm2)

Mean T

score

femoral

neck

Mean BMD

lumbar spine

(g/cm2)

Mean T

score lumbar

spine

Mean BMD

femoral neck

(g/cm2)

Mean T score

femoral neck

………………….Mean+/-SDd……………………

Total

group

1.24+/-0.11

0.27+/-0.95

1.08+/-0.09

0.78+/-0.64

1.14+/-0.10

–0.44+/-0.86

0.97+/-0.10

–0.50+/-0.80

Small

frame

1.24+/-0.05

0.37+/-0.39

1.09+/-0.09

0.93+/-0.73

1.12+/-0.10*

–0.69+/-0.84

0.96+/-0.10*

–0.15+/-0.87

Medium

frame

1.20+/-0.10

–0.03+/-0.96

1.08+/-0.09

0.70+/-0.62

1.23+/-0.08

0.21+/-0.70

1.02+/-0.07

0.31+/-0.54

Large

frame

1.28+/-0.14

0.54+/-1.11

1.08+/-0.08

0.78+/-0.68

1.15+/-0.01

–0.46+/-0.07

0.925+/-0.07

–0.46+/-0.57

NOTE. Frame Size: Wrist circumference measured distal to the styloid

process of the radius and ulna was compared with height

without shoes using the chart for small, medium, or large frame size as

established by Linder and Linder (21).

a Small-framed women.

b Medium-framed women.

c Large-framed women.

d SD=standard deviation.

* Results significant at P<.01 using independent sample t test.

Only the length of time reported in current physical activity was

significantly different between groups. The NW group exercised an

average of 4.35 hours/week compared with 2.46 hours/week for

the LW group (Table 1). The NW group more often reported that

they participated in multiple athletic, exercise, or workout events,

whereas the LW group was more likely to consider brisk walking

or a single exercise or workout event as their physical activity.

Physical activity in the NW group showed a significant and positive

correlation with the BMD of the lumbar spine (r=0.562; P<.01);

however, no positive correlation was seen in the LW group. There was

no significant difference between groups in the mean amount of

energy, calcium, carbohydrate, protein, fat, or fiber consumed (Table

1) and no correlations to BMD levels.

Results of BMD levels and T scores of the femoral neck and

lumbar spine between groups were significantly different in the

small-framed women but not for the medium- or large-framed

women (Table 2). To investigate the nature of this difference, further

analysis involved looking at individual T scores for all 61 participants.

In the NW group, two medium-framed women had a T score of

the lumbar spine (–1.10 and –1.28) in the osteopenia range. None

of the NW group women had T scores in the osteopenia range for

the femoral neck. Nine small-framed women of the LW group had

T scores in the osteopenia range for the lumbar spine (range:

–1.02 to –2.29). Three small-framed women (two with osteopenia

of the spine) in the LW group had T scores in the osteopenia range

for the femoral neck (range: –1.01 to –1.26). A T score of 0 to –1

standard deviation is within normal limits. A T score of >–1.0 but

<–2.5 is indicative of low bone mass or osteopenia, and a T score

below –2.5 is indicative of osteoporosis (22,23).

Discussion

Professor E. Dent of London is reported as saying that

“senile osteoporosis is a pediatric disease” (2). That is that failure to

reach peak bone mass during developmental years may predispose

the individual to osteoporosis in old age, especially as bone

mass is lost with aging.

…………………………..

Limitations of the study include nonrandom selection of volunteers

who may be more prone to healthy behaviors, leading to better

bone health than the general public. Also, accuracy or bias of the

self-reporting tools used such as the food intake, exercise history,

and eating disorder inventories may lead to under or over

reporting, distortion, denial, and dishonest reporting or minimization of

symptoms. Furthermore, no WHO T score definition has been

established for premenopausal women; however, probably for lack of

other guidelines, the T score definition for postmenopausal women

is becoming universally used as a screening tool in clinical

practice for all age groups (28) to detect low bone mass.

………………………………..

Alan Pater, Ph.D.; Faculty of Medicine; Memorial University; St. 's, NL

A1B 3V6 Canada; Tel. No.: (709) 777-6488; Fax No.: (709) 777-7010; email:

apater@...