rs174541 — FADS1 FADS1 C>G (delta-5 desaturase depth)

FADS1 rs174541 — Delta-5 Desaturase Depth

Your body's ability to build long-chain omega-3 and omega-6 fatty acids from dietary precursors hinges on a single enzyme: delta-5 desaturase¹¹ delta-5 desaturase
FADS1 (Fatty Acid Desaturase 1) — the enzyme that adds a double bond at the fifth carbon position, converting DGLA to arachidonic acid in the omega-6 pathway and eicosatetraenoic acid (ETA) to EPA in the omega-3 pathway. rs174541 is an intronic variant in the FADS gene cluster on chromosome 11q12.2 that acts as an independent regulator of how much FADS1 enzyme your cells make. The C allele dampens FADS1 expression, reducing the throughput of both the omega-6 pathway (less arachidonic acid from dietary linoleic acid) and the omega-3 pathway (less EPA from plant-derived ALA). Because the C allele also affects circulating triglyceride concentrations, this variant sits at the junction between fatty acid metabolism and broader cardiometabolic risk.

The Mechanism

rs174541 sits within FADS1's intronic regulatory architecture, in high linkage disequilibrium with the established functional cluster of FADS1 variants (rs174546, rs174547, rs174548, rs174537). Intronic variants in this region influence transcription factor binding sites and enhancer elements between FADS1 and FADS2 — the C allele at rs174541 tracks with reduced FADS1 mRNA levels and lower delta-5 desaturase enzyme activity across liver and blood cells.

The functional consequence plays out across two metabolic pathways simultaneously. In the omega-6 pathway: dietary linoleic acid (LA) → GLA → DGLA → [delta-5 desaturase] → arachidonic acid (AA). Reduced FADS1 activity means more DGLA accumulates and less AA is produced. In the omega-3 pathway: plant ALA → stearidonic acid → ETA → [delta-5 desaturase] → EPA. Again, the rate-limiting step is impaired, meaning less EPA is synthesised from the plant-sourced precursor. Neither pathway can compensate for the other — both require the same enzyme.

The Evidence

A Bayesian quantitative trait nucleotide analysis²² Bayesian quantitative trait nucleotide analysis
Voruganti et al. Variants in CPT1A, FADS1, and FADS2 are Associated with Higher Levels of Estimated Plasma and Erythrocyte Delta-5 Desaturases in Alaskan Eskimos. Front Genet, 2012 in 761 Alaskan Eskimos assigned rs174541 a posterior probability >0.8 for functional effect on erythrocyte delta-5 desaturase activity — the strongest statistical evidence available in a Bayesian framework for a variant being causally linked to its phenotype, not merely in LD with the causal site.

The broader FADS1 locus evidence is overwhelming. A landmark GWAS in the InCHIANTI study³³ landmark GWAS in the InCHIANTI study
Tanaka et al. Genome-wide association study of plasma polyunsaturated fatty acids in the InCHIANTI Study. PLoS Genet, 2009 of 1,075 Italian adults found that FADS1 cluster variants explain 18.6% of all additive variance in circulating arachidonic acid (p=5.95×10⁻⁴⁶), by far the largest explained variance for any common PUFA-metabolism variant. The CHARGE Consortium meta-analysis⁴⁴ CHARGE Consortium meta-analysis
Lemaitre et al. Genetic loci associated with plasma phospholipid n-3 fatty acids. PLoS Genet, 2011 across 8,866 European ancestry participants confirmed that FADS1 minor alleles are the dominant genetic predictor of lower circulating EPA (p=5×10⁻⁵⁸) and higher plant ALA (p=3×10⁻⁶⁴).

Beyond fatty acid ratios, FADS1 variants have direct consequences for clinical lipid panels. In 21,004 Japanese individuals⁵⁵ 21,004 Japanese individuals
Nakayama et al. A single nucleotide polymorphism in the FADS1/FADS2 gene is associated with plasma lipid profiles. Hum Genet, 2010, the C allele at the tightly linked rs174547 was significantly associated with higher triglycerides (p=1.5×10⁻⁶) and lower HDL-C (p=0.03), demonstrating that FADS1 reduced activity has effects visible on a standard fasting lipid panel — not just on specialised PUFA measurements. A study of 8,842 Korean adults⁶⁶ study of 8,842 Korean adults
Lee et al. Functional Impact of the FADS1 rs174546 Single Nucleotide Polymorphism on Serum Lipid Levels. Mol Nutr Food Res, 2024 quantified this: the FADS1 minor allele increases fasting serum triglycerides by 6.48 ± 1.84 mg/dL per allele, mediated through reduced LC-PUFA production and downstream effects on VLDL assembly and clearance.

Practical Actions

For C allele carriers, the core problem is that dietary plant-based omega-3 sources (flaxseed, chia, walnuts, canola oil) supply ALA which requires FADS1 to reach EPA. When FADS1 activity is reduced, that conversion chain slows — the ALA enters the bloodstream but stalls before reaching EPA. Direct supplementation with preformed EPA and DHA from marine or algae-based sources entirely bypasses the impaired step. The dosage depends on genotype: CT carriers benefit from 1–2 g EPA+DHA daily; CC homozygotes need 2–4 g to overcome the more complete impairment.

The triglyceride finding adds a monitoring dimension. If you carry the C allele and have other cardiovascular risk factors, a fasting lipid panel captures the clinical footprint of this genotype — elevated triglycerides and reduced HDL are the measurable downstream signal of impaired FADS1 activity.

Interactions

rs174541 is in high linkage disequilibrium (r² >0.8) with the established FADS1 functional cluster including rs174547, rs174548, rs174546, and rs174537. Users may carry risk alleles at multiple sites on the same haplotype — carrying the C allele at rs174541 in combination with risk alleles at rs174548 and rs174547 increases the probability of being on the full reduced-function FADS1 haplotype. No additional effect beyond what each individual variant predicts is needed for interpretation, as the variants tag the same underlying expression phenotype.

The ELOVL2 gene variant rs17606561 (also in the platform) encodes elongase 2, which converts EPA to DHA. A user who carries both FADS1 reduced-activity alleles and an ELOVL2 impairment faces a double block in the ALA → EPA → DHA pathway, potentially producing the most severe DHA deficiency of any single-enzyme genotype combination. For such users, a DHA-specific supplement target (≥500 mg DHA per day) matters beyond total EPA+DHA.