Dry Eye Dx and Tx
Omega Essential Fatty Acids: Friend or Foe?
BY WILLIAM TOWNSEND, OD, FAAO
Systemic omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) have gained popularity as a therapy for lipid-based dry eye (Lemp et al, 2012; Nichols et al, 2011). They are also prescribed for other ocular conditions such as age-related macular degeneration (Pinna et al, 2007; Aslam et al, 2013) and for preventing or treating cardiovascular disease (SanGiovanni and Chew, 2005; Mozaffarian and Wu, 2013).
PUFAs Called Into Question
In “Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial,” Brasky et al (2013) reported, “In this large, prospective trial, high plasma phospholipid concentrations of long-chain omega-3 PUFA were associated with statistically significant increases in prostate cancer risk.” As a practitioner who takes and often prescribes PUFAs, this was surprising and concerning.
The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was a randomized, prospective, double-blind study initiated in 2001 and “designed to determine whether selenium and vitamin E decrease the risk of prostate cancer in healthy men” (Bransky et al, 2013). The original study description had no mention of omega fatty acids.
Bransky et al conducted their study as a “case-cohort design nested within SELECT.” They identified two groups of study subjects: those who were diagnosed with prostate cancer, and a control group not diagnosed with the disease. Venous blood samples were collected from both groups and analyzed for various PUFAs. That data was correlated with the incidence of prostate cancer (Furhman, 2013). They reported that men who had the highest levels of long-chain PUFAs had an increased risk for low-grade, high-grade, and total prostate cancer (Furhman, 2013).
A Closer Look at the Data
In evaluating this study and the ensuing publication, we must address several issues:
1. The SELECT study was not designed to evaluate the association between PUFAs and prostate cancer; it addressed the protective effect of selenium and vitamin E.
2. A single blood test prompted the cohort study’s conclusions. Developing cancer secondary to dietary factors occurs over years. Taking multiple blood draws over an extended period would better represent long-term dietary intake (Turgeon et al, 2013).
3. Studies specifically designed to target the relationship between PUFAs and prostate cancers have mixed results. In a meta-analysis, Chua et al (2013) reported that high serum levels of long-chain omega-3 PUFAs were associated with reduced total prostate cancer risk, while high blood levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) might be linked to increased risk for high-grade prostate cancer.
4. Populations with inherently high dietary PUFA intake via fish consumption have lower rates of prostate cancer (Chua et al, 2013; Dewailly et al, 2003).
5. Symanski et al (2010) reported a significant (63 percent) reduction in prostate cancer-specific mortality with PUFA intake.
Good evidence suggests that dietary PUFAs may reduce the incidence of or mortality associated with prostate cancer. Given this data, we need to weigh the advantages and real risk for precipitating prostate cancer prior to discontinuing or initiating PUFAs for any reason, including for dry eye states. CLS
For references, please visit www. clspectrum.com/references.asp and click on document #215.
Dr. Townsend practices in Canyon, Texas, and is an adjunct professor at the University of Houston College of Optometry. He is president of the Ocular Surface Society of Optometry and conducts research in ocular surface disease, lens care solutions, and medications. He is also an advisor to Alcon, B+L, CooperVision, Tearlab Corporation, and Vistakon. Contact him at firstname.lastname@example.org.