In the news: Vitamin A & Dark Adaptation in AMD; Circulating Omega-3 Linked to Lung Function

Moderate Dose Vitamin A May Improve Dark Adaptation in iAMD Over Time

Previous studies have reported that high dose vitamin A (50,000 IU) may improve impaired dark adaptation (ability of the retina to transition from the light-adapted or photopic state to the dark adapted or scotopic state) in those with intermediate stage age-related macular degeneration (iAMD).

A small but potentially meaningful new study(1) from the National Eye Institute now suggests that a lower dose of vitamin A (16,000 IU) can also significantly improve dysfunctional dark adaptation, though not in patients with reticular pseudodrusen – RPD, district lesions that occur in the subretinal space.

In the study, five patients with iAMD and with no RPD (AMD group) and seven with RPD (RPD group) received 16,000 IU of Vitamin A palmitate for 8 weeks. Patients were assessed at baseline, 4, 8 and 12 weeks on scotopic thresholds, dark adaptation, best-corrected and low luminance visual acuities and the low-luminance quality of life questionnaire.

Rod intercept time – which measures the amount of time it takes for eyes to adapt to darkness – improved significantly in the AMD group, with a mean change of -1.1 minute after 4 weeks and -2.2 minutes after 8 weeks of supplementation (p<0.001 for both time points).

The DA cone plateau also significantly improved (specifically, a more sensitive cone threshold) at 4 weeks (p=0.026 and at 8 weeks (p=0.001). The improvements in dark adaptation function seen at 4 and 8 weeks remained significant at 12 weeks.

In contrast, none of the measures improved significantly at any time point in the RPD group despite blood levels of vitamin A increasing during the study.

The authors postulate that in the iAMD group, “photoreceptors may be amenable to treatment and that dysfunction can be at least partially reversed”, while in the RPD group “the dysfunction could be due to a loss of photoreceptors or alterations that are beyond rescue.”

The authors point out that the RPD group in this study had significantly lower rod intercept time values at baseline, and showed no improvement after three months of vitamin A supplementation. The researchers also indicated that the higher variability observed in the functional parameters for this group may also contribute to the lack of improvement.

Omega-3 May Help Protect Lung Function

According to a two-part study(2)(4), higher blood levels of omega-3 fatty acids, particularly DHA, are associated with a slower rate of lung function decline.

In the first part of the study – a longitudinal analysis of over 15,000 participants from the National Health Lung and Blood Institute Pooled Cohorts Study – higher DHA levels were also linked with a lower likelihood of restricted airflow from the lungs.

One standard deviation higher DHA blood level correlated with counteracting about 25% of the additional restricted airflow annual decline in current smokers vs. non-smokers and nearly all the additional decline in former smokers(3). The DHA blood level associated with counteracting this decline is achievable with a high-fish diet or omega-3 supplements.

The second analysis used a technique called Mendelian randomization to examine a causal relationship between omega-3 blood levels and lung health. Overall, the genetics-based analysis, which involved 500,000 United Kingdom Biobank participants, supported the observations from the longitudinal analysis that DHA was associated with slower lung function decline.

References

1. Pfau K, et al. Low-dose supplementation with retinol improves retinal function in eyes with age-related macular degeneration but without reticular pseudodrusen. Retina. Online ahead of print June 9, 2023.
2. Harris E. Higher levels of omega-3 fatty acids linked to improved lung health. JAMA ePub Aug, 2023.
      
3. Sun Y, et al. The protective effect of omega-3 fatty acids in attenuating lung function decline. Am J Resp Crit Care Med. Article in Press Aug, 2023.
      
4. Patchen BK, et al. Investigating associations of omega-3 fatty acids, lung function decline, and airway obstruction. Am J Respir Crit Care Med. Epub July 20, 2023.