Vitamin Information Center

Case Control Studies
Definition
Studying infrequent events, such as death from cancer,
using randomized clinical trials or other controlled
prospective studies requires that large populations be
tracked for long periods in order to observe disease
development. Case-control studies use patients who
already have a disease or other condition and look back
to see if there are characteristics of these patients that
differ from those who don’t have the disease. The casecontrol
study provides a much cheaper and quicker
study of risk factors. If the evidence found is convincing
enough, then resources can be allocated to more “credible”
and comprehensive studies. The case-control study
begins with the identification of an outcome or effect
and a number of potential causative factors. A group
of cases which exhibit the outcome under investigation
is selected. A number of control subjects (or controls)
who do not exhibit the outcome or effect under investigation
are then chosen. These controls should match the
cases as closely as possible with respect to the non-risk
variables; this allows the proposed non-risk variables to
be ignored in the analysis. Sometimes more than one
control group is used. The case and control groups are
then compared for the proposed causal factors, and statistical
analysis is used to estimate the strength of association
of each factor with the studied outcome.
Case-control studies are a valuable investigative tool,
providing rapid results at low cost, but caution should
be exercised unless results are confirmed by other, more
robust evidence.

The benefits of a combined vitamin D3 and calcium for bones, reported to stop or slow bone loss, may extend for up to 18 months after stopping supplementation, suggests a new study from Australia.

The increases in bone mineral density of about 1.65 per cent observed in men after receiving vitamin D and calcium supplements were still evident 18 months after the men stopped taking the supplements, researchers report in this month’s American Journal of Clinical Nutrition.

The study shows that elderly men, a population that is often overlooked in bone health studies, could also benefit from daily supplements of fortified milk.

Much focus has been on the vitamin D and calcium combination for bone health in women since elderly females are four times as likely to develop osteoporosis than their male counterparts. The new study, which follows on from an earlier study in the journal Bone (doi: 10.1016/j.bone.2006.04.003), reports that elderly men benefited from daily supplements of fortified milk.

Osteoporosis is estimated to affect about 75m people in Europe, the USA and Japan. According to the International Osteoporosis Foundation, the total direct cost of osteoporotic fractures is €31.7bn in Europe, and 17.5bn in the US (2002 figure).

Robin Daly and co-workers from Deakin University in Melbourne followed 109 who had completed the earlier study for a further 18 months, during which no more fortified milk was provided.

The benefits on bone mineral density observed in the on the hip bone (femoral neck) and wrist (ultra-distal radius) at the end of the intervention of 1.8 and 1.5 per cent, respectively, were still evident 18 months later.

Furthermore, non-significant increases at the total hip of 0.8 per cent were also sustained.

“The average total dietary calcium intake in the milk supplementation group at follow-up approximated recommended amounts for Australian men older than 50 (1000 mg/d) but did not differ significantly from that in the control subjects (1021 versus 890 mg/d),” stated the researchers for clarification.

“Supplementation with calcium- and vitamin D3-fortified milk for two years may provide some sustained benefits for BMD in older men after withdrawal of supplementation,” they concluded.

The researchers reported in the earlier study in Bone that, due to the complicated nutritional mixture of the milk, it was not known whether the benefits were due to vitamin D3, calcium, or a combination of these plus other nutrients. They did state however that the results show a reduction in bone resorption in this elderly male population sample.

The fortified milk used in the initial intervention contained 500 milligrams of calcium (milk calcium salt NatraCal) and 400 International Units (IU) of vitamin D3 (DSM Nutritional Products), and was formulated by Murray Goulburn Co-operative in Brinswick, Australia.

Some countries, like Canada, already fortify their milk and a 250 ml cup provides about 90 IU of vitamin D. In the UK, where milk is not fortified, a 250 ml cup contains only a trace of the vitamin.

The 1999 USDA survey on food intakes by individuals reported that less than 15 per cent of over-sixty year-old men were meeting their recommended daily intake of calcium.

Source: American Journal of Clinical Nutrition
March 2008, Volume 87, Number 3, Pages 771-777
“The skeletal benefits of calcium- and vitamin D3-fortified milk are sustained in older men after withdrawal of supplementation: an 18-mo follow-up study”
Authors: R.M. Daly, N. Petrass, S. Bass, C.A Nowson