Deep Dive: Omega-3s and Vitamin D—The Evidence¶
Reading time: ~5 minutes
Prerequisite: Chapter 2.7 (Nutrition for Longevity)
The Big Picture¶
Of all supplements, omega-3 fatty acids and vitamin D have the most research behind them. But "most research" doesn't mean "proven benefits for everyone." Here's what we actually know.
Omega-3 Fatty Acids¶
What They Are: EPA and DHA, long-chain fatty acids found primarily in fatty fish. ALA (from plants) converts poorly to EPA/DHA.
The Evidence:
| Outcome | Evidence Level |
|---|---|
| Triglyceride reduction | Strong (at high doses) |
| Cardiovascular disease prevention | Mixed (benefits in some populations) |
| Cognitive decline prevention | Weak/inconsistent |
| Inflammation reduction | Moderate |
| Depression improvement | Modest |
Key Studies:
- REDUCE-IT: High-dose EPA (4g/day) reduced cardiovascular events in statin users with elevated triglycerides
- VITAL: 1g/day fish oil didn't reduce major cardiovascular events overall, but may benefit those with low baseline fish intake
Practical Takeaway:
- If eating <2 servings fatty fish weekly: supplementation may help
- If triglycerides elevated: higher doses (2-4g) may be beneficial (with physician guidance)
- Standard 1g supplements: uncertain benefit for most people
Vitamin D¶
What It Is: A hormone precursor synthesized from sunlight or obtained from food/supplements. Widespread deficiency, especially in northern latitudes, darker skin, and elderly.
The Evidence:
| Outcome | Evidence Level |
|---|---|
| Bone health (with calcium) | Strong |
| Fall prevention in elderly | Moderate |
| Mortality reduction | Modest in deficient populations |
| Cancer prevention | Weak/inconsistent |
| Immune function | Plausible mechanism; mixed trial results |
Key Studies:
- VITAL: No reduction in cancer or cardiovascular events with 2000 IU/day
- Meta-analyses suggest modest mortality reduction in deficient populations
Practical Takeaway:
- Test before supplementing if possible
- If deficient (<30 ng/mL): supplementation clearly helpful
- If sufficient: additional supplementation unlikely to help
- 1000-2000 IU/day is reasonable if deficiency suspected and testing unavailable
The Honest Assessment¶
Neither Is a Magic Bullet
The excitement around these supplements often exceeds the evidence. Large trials have generally shown modest or null effects in adequately nourished populations.
Context Matters
Benefits appear strongest when:
- Deficiency exists (vitamin D)
- Dietary intake is low (omega-3s)
- Specific conditions are present (elevated triglycerides for omega-3s)
Food First
For most people, prioritizing dietary sources (fatty fish, sun exposure where safe) is preferable to defaulting to supplements.
What This Means for Coaches¶
- Stay in scope: Don't recommend specific doses. That's for healthcare providers.
- Encourage testing: Vitamin D levels guide supplementation decisions.
- Food first: Support dietary changes before supplement solutions.
- Honest expectations: These aren't miracle supplements. Modest effects in specific contexts.
Key Takeaway¶
Omega-3s and vitamin D are among the most-studied supplements, with genuine benefits in specific contexts (deficiency, elevated triglycerides), but large trials show modest effects in already-nourished populations, supporting a food-first approach with targeted supplementation when indicated.
References¶
- Bhatt DL, et al. Cardiovascular Risk Reduction with Icosapent Ethyl (REDUCE-IT). NEJM. 2019.
- Manson JE, et al. VITAL Trial. NEJM. 2019.
- Autier P, et al. Vitamin D status and ill health: a systematic review. Lancet Diabetes Endocrinol. 2014.
- Mozaffarian D. Fish oil and omega-3 fatty acids. UpToDate. 2024.