Chemistry Reference
In-Depth Information
irritable bowel syndrome in Europe and the USA (Vesa et al., 2000). Many
commercial dairy products and other foods contain very high concentrations
of lactose which are introduced in manufacturing, so that lactose is more
widespread in the diet than it was for that same person's ancestors. Lactose
tolerance testing can be a useful way of detecting lactose malabsorption and
enabling avoidance of the cause. In countries such as Finland, which has a
high frequency of lactase non-persistence in comparison with the rest of
northern Europe, commercial low-lactose products are readily available
(Harju, 2003).
Many studies have attempted to demonstrate the health benefits of milk
consumption in lactase-persistent people, e.g. by providing protection against
osteoporosis as well as contrasting studies that have claimed adverse effects of
lactase persistence and associated high milk consumption. This research has
so far failed to produce reliable and reproducible results in either direction. It
has been suggested that lactase-persistent individuals may be at reduced risk
of developing osteoporosis (Obermayer-Pietsch et al., 2004); however, a
recent study of post-menopausal women found no significant increase of
osteoporosis in 'molecularly defined' lactose maldigesters. The maldigesters
were found to consume less milk but tended to have an increased intake of
calcium supplements (Enattah et al., 2005a). The same group found that
'molecularly defined' lactose maldigestion did, however, increase the risk of
developing osteoporosis in individuals aged over 85 (Enattah et al., 2005b).
Some studies suggest an association of lactase persistence with ovarian
cancer, said to be caused by the toxicity of galactose to oocytes (Meloni et al.,
1999); however a meta analysis combining data from a number of studies
showed association only in cohort and not case-control designed research
(Larsson et al., 2006). Likewise, association studies of lactase persistence with
diabetes produce similarly conflicting results (Meloni et al., 2001; Enattah
et al., 2004). These often-contradictory findings are difficult to evaluate
because of the high risk of confounding effects such as mixed ancestry and
dietary intake.
6.12.
Genetic Testing
The discovery of the new lactase persistence-associated SNPs in sub-Saharan
African and Middle Eastern populations, along with the observations dis-
cussed above makes the development of a universal genetic test for lactase
persistence currently unfeasible. Furthermore, both research groups who
identified new lactase persistence-associated SNPs found that there were
many individuals without a -13.9/-14.0 kb variant allele but who were lactase
persistent, which indicates that there are other alleles yet to be found, and
