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In the news: Omega-3s & Colorectal Cancer Precursors; Dietary Zinc Important in Wet AMD Omega-3s & Colorectal Cancer Precursors; Dietary Zinc Important in Wet AMD

Omega-3 May Help Some Cut Colorectal Cancer Risk

Earlier this year, the primary findings of the large-scale placebo-controlled prevention trial, the Vitamin D and Omega-3 Trial (VITAL), were reported. With the notable exception for participants with low fish intake at baseline, VITAL found no reduction in the incidence of major cardiovascular events with omega-3 (ω-3) supplementation.

In addition, no overall benefit for omega-3 in lowering cancer risk was found, although the number of cases was too small for a well-powered analysis specifically on colorectal cancer risk.

Experimental data indicate that marine omega-3 fatty acids have potent anti-inflammatory effects and may protect against colorectal cancer (CRC), the fourth most common cancer in the US. Several prospective studies also indicate that these fatty acids may be chemo-protective in the early stage of CRC development.

These data provided the rationale for a prespecified ancillary study (1) in VITAL examining the effect of omega-3 supplementation (460 mg EPA, 380 mg DHA) on conventional adenomas and serrated polyps, 2 major groups of CRC precursors. The study included 25,871 adults, who were treated a median 5.3 years.

The findings of the prespecified ancillary study showed that supplemental omega-3 did not reduce risk of conventional adenomas or serrated polyps in the cohort as a whole.

However, in secondary analyses a beneficial association was observed among participants with low plasma levels of omega-3 index at baseline. A 24% lower risk of conventional adenomas was seen in those with an index of 2.5% or less at baseline. (The omega-3 index is the percentage of EPA and DHA present among all fatty acids in red blood cell membranes).

The omega-3 treatment was also associated with a 41% lower risk of adenomas in African American persons, whereas no association was found in other racial/ ethnic groups. This difference can’t be explained by a variation in omega-3 status prior to randomization because baseline plasma levels of EPA and DHA and fish consumption did not show major differences across racial/ethnic groups.

In short, omega-3 daily supplementation with marine omega-3 fatty acids appears not to reduce the risk of colorectal premalignant lesions in the average-risk US population. However, African Americans and individuals with low plasma levels of omega-3 may benefit. The authors note that a similar beneficial interaction between omega-3 treatment and baseline omega-3 status (low fish intake) was found for cardiovascular events in VITAL.

Zinc for Those with Wet AMD on Anti-VEGF

Supplemental zinc along with antioxidants have been shown to slow AMD progression, but little is known about the impact of these nutrients in patients with late-stage disease undergoing anti-VEGF treatment.

To learn more, Australian researchers explored the relationship between dietary zinc consumption and clinical outcomes in 547 patients with neovascular AMD (2).

Participants whose daily zinc intake was below vs. above 8.1 mg had greater odds of having subretinal fluid – an association that was stronger in those with at least 6 months of anti-VEGF treatment.

Increased central macular thickness was also seen in patients with the lowest 25% of zinc intake compared to those in the upper 75% of intake. These findings suggest that higher zinc intake can favorably influence clinical outcomes in those with neovascular AMD receiving anti-VEGF treatment.

References

1. Song M, et al. Effect of supplementation with marine ω-3 fatty acid on risk of colorectal adenomas and serrated polyps in the US general population. A prespecified ancillary study of a randomized clinical trial. JAMA Oncol. Published online November 21, 2019.
2. Detaram HD, et al. Dietary zinc intake is associated with macular fluid in neovascular age-related macular degeneration. Clin Exp Ophthalmol. Epub Oct 8, 2019.