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In the news:Omega-3 & Blood Pressure Vitamin A & Dark Adaptation in AMD

A Clearer Picture of Optimal ω3 Intake for Blood Pressure Reduction

Current evidence generally supports the use of omega-3 (ω3) fatty acids EPA and DHA in lowering blood pressure, but the shape of the dose response relationship has been unclear – linear or non-linear?

Previous meta-analyses examining the association between ω3 intake and blood pressure have been unable to reveal a significant dose-response relationship or have shown conflicting trends.

Using a recently developed model for dose- response meta-analyses, researchers included 71 trials, involving 4973 individuals to look for the optimal fish oil dose lowering blood pressure(1). The studies included examined the effects of DHA, EPA or both from whole foods and supplements at doses of 1-5 grams daily.

A J-shaped curve was found, with the optimal combined intake of ω3 fatty acids for blood pressure lowering between 2 and 3 grams per day for the general population. At 2-3 grams daily of ω3 fatty acids, the mean decrease was -2.61 mmHg for systolic blood pressure and -1.64 to -1.80 mmHg for diastolic. For those with hypertension, 3 grams daily was associated with a mean decrease in systolic pressure of 4.5 mmHg.

Looking at pre-specified subgroups, the researchers found a stronger and nearly linear dose-response of ω3 fatty acids among hypertensive, hyperlipidemic and older individuals. The authors concluded that ω3 fatty acid intake above the recommended 3 grams daily may be associated with additional benefits in blood pressure-lowering among groups at high risk for cardiovascular diseases.

Pilot Study: Functional Impact of Low Dose Vitamin A in AMD

Dark adaptation refers to the capability to see in low light or darkness after exposure to bright light. How the eyes adapt to darkness can be a key indicator of retinal health, and dark adaptation can be altered in certain ocular diseases such as age-related macular degeneration (AMD). Dark adaptation occurs over a large range of luminance and involves both cone and rod photoreceptors. One reliable measure of rod response and dark adaption response is the rod-intercept time (RIT) – the time required for rod sensitivity to recover by 3 log units after exposure to bright light (called bleaching).

Using RIT and other measures, researchers from the National Eye Institute examined the functional impact of oral vitamin A on dark adaptation in a small number of participants with AMD separated into those without and with reticular pseudodrusen (associated with more severe disease)(2). Both the AMD and RPD groups received 15,000 IU vitamin A palmitate supplements daily for 8 weeks and were followed another 4 weeks after stopping supplementation.

RIT improved significantly in the AMD group (-1.1 min after 4 weeks and -2.2 min after 8 weeks), both p<0.001. The improvement to RIT declined after vitamin A supplementation ceased, but a residual treatment effect could be measured.

In contrast, no significant improvement with vitamin A was seen in the RPD group.

According to the researchers, the result supports a mechanism where a diseased Bruch’s membrane serves as a barrier between the systemic circulation and the photoreceptors. Increasing systemic vitamin A availability through supplementation is thought to partially overcome that barrier in less severely affected eyes and improve dark adaptation. The authors stress that this is a pilot study, and more research is required to determine long-term effects of vitamin A.

References

1. Zhang Xin, et al. Systematic Review and Meta-Analysis. Omega‐3pPolyunsaturated fatty acids intake and blood pressure: A dose‐response meta‐analysis of randomized controlled trials. J Am Heart Assoc. Epub June 7, 2022.
2. Hess K, et al. The functional impact of low dose vitamin A supplementation in AMD with and without reticular pseudodrusen. ARVO Annual Meeting Abstract. IOVS 63:376, June 2022.