ZINC-GENETICS INTERACTION

Increasing dietary zinc intake appears to decrease the risk of late stage age-related macular degeneration (AMD), but only among persons with a high genetic risk, according to analyses of data from European-derived population-based cohorts.

The research was presented by Paul R Healey MD, PhD at the 2015 annual meeting of the Association for Research in Vision and Ophthalmology in Denver, USA.

The effect of genetic risk on the relationship between dietary zinc intake and incident late stage AMD was investigated using data from the Blue Mountains Eye Study and the Rotterdam Study. The pooled population included 5,246 subjects who were categorised into four genotype groups based on numbers (0, 1, 2) of Compliment Factor H (C) and Age-Related Maculopathy Susceptibility 2 (A) risk alleles: Group 1 (C01, A0), Group 2 (C2, A0), Group 3 (C01, A12), Group 4 (C2, A12).

Genotype distribution was similar in the two populations, with the highest frequencies (53 per cent to 55 per cent) in Group 1, the lowest AMD risk group, and only about a five per cent frequency in Group 4, the highest risk group. The 15-year cumulative incidence of late stage AMD was five per cent in the overall population, 2.7 per cent in Group 1, 8.2 per cent in Group 2, 6.2 per cent in Group 3, and 19.7 per cent in Group 4. In a regression analysis adjusting for age, smoking and zinc intake, the risk of developing AMD was nearly 12-fold higher in Group 4 than in Group 1.

DIETARY INTAKE

When each genotype group was divided into quartiles based on daily dietary zinc intake, a relationship between dietary zinc intake and late stage AMD risk was seen only in Group 4, and it showed a reasonably strong dose-response effect. Compared with persons having the lowest interquartile zinc intake (7.5mg/day), those with the highest intake (15.3mg/day) had a very substantial 80 per cent lower risk of developing late stage AMD, reported Dr Healey, Clinical Associate Professor of Ophthalmology, University of Sydney, Australia.

“Further study is needed to determine whether we should be encouraging people to change their diet to increase their zinc intake. While we found there was no harm associated with higher zinc intake in terms of mortality or AMD risk, a very small risk that may not be evident in smaller studies may be amplified in a large population,” he said.

Dr Healey also pointed out that the genotype distribution in the two population-based studies differs substantially from what was seen in AREDS. “The majority of cases of late stage AMD occur in the low risk genotypes, and that is important when thinking about genetic screening or specific treatment,” he said.

Paul R Healey: phealey@glaucoma.net.au