🔬 The VITAL Trial: Large-Scale Evaluation of Vitamin D and Omega-3
What the largest RCT showed about cancer and cardiovascular disease
VITAL (Vitamin D and Omega-3 Trial) is one of the largest randomized placebo-controlled trials in the world, conducted by Harvard Medical School and Brigham and Women's Hospital. It included more than 25,000 adults (men 50+ and women 55+), followed for a median of 5.3 years. The goal was to test whether vitamin D and Omega-3 supplements reduce the risk of cancer and major cardiovascular events.
Trial design
Participants were randomly assigned to four groups in a 2×2 design:
| Group | Vitamin D | Omega-3 |
|---|---|---|
| 1 | 2000 IU/day | 1 g/day (fish oil) |
| 2 | 2000 IU/day | Placebo |
| 3 | Placebo | 1 g/day |
| 4 | Placebo | Placebo |
Primary endpoints were invasive cancer and major cardiovascular events (myocardial infarction, stroke, cardiovascular death). Results were published in the New England Journal of Medicine in late 2018.
Vitamin D and cancer
The overall cancer result was null: vitamin D did not reduce the incidence of invasive cancer in the general group. However, in subgroup analysis, people with normal weight (BMI <25) showed a significant risk reduction (~25%). No effect was seen in people with obesity.
- Overall cancer mortality did not differ between groups.
- People with BMI <25 had a lower cancer risk.
- Cancer mortality fell in the normal-weight subgroup.
- Subgroup data are considered hypothesis-generating, not conclusive.
Vitamin D and cardiovascular disease
The overall result was null: vitamin D did not reduce the incidence of cardiovascular events in the general group. No significant reduction was seen in any major measure (myocardial infarction, stroke, cardiovascular death).
Omega-3 and results
Omega-3 was overall neutral for the primary endpoint. However, there was a significant reduction in the risk of myocardial infarction (~28%) and cardiovascular death among those who did not regularly eat fish (secondary analysis). No significant reduction was seen for stroke.
- Total cardiovascular events were not reduced.
- Infarction risk fell in people with low fish intake.
- The effect was stronger in African Americans and non-regular fish eaters.
- Subgroup results are hypothesis-generating.
Overall findings
| Outcome | Vitamin D | Omega-3 |
|---|---|---|
| Invasive cancer | No reduction overall | Not a primary endpoint |
| Cancer (BMI<25) | Reduction (~25%) | — |
| Cardiovascular | No reduction | No reduction overall |
| Infarction (low fish) | — | Reduction (~28%) |
The main finding: in healthy adults with normal levels, vitamin D and Omega-3 supplements do not provide convincing overall protection against cancer and heart attacks. Benefit appears in specific subgroups (deficiency, low fish intake, normal weight) and is not conclusive for everyone.
Practical takeaways
- Check your vitamin D level — 25(OH)D; ~75–100 nmol/L (30–40 ng/mL) is usually considered optimal.
- With deficiency, supplements are justified; with normal levels, extra benefit is not proven.
- Omega-3 is useful with low fish intake (2 servings of fatty fish per week is recommended).
- VITAL doses: vitamin D 2000 IU/day, Omega-3 1 g/day.
- Do not replace medications and lifestyle with supplements — VITAL confirmed this.
Food: sources
| Nutrient | Foods | Content/portion | Comment |
|---|---|---|---|
| Vitamin D | Salmon, mackerel, eggs, mushrooms | ~400–600 IU/100 g salmon | Fatty fish is the main source |
| Omega-3 (EPA/DHA) | Salmon, sardines, mackerel | ~1–2 g/100 g | 2 servings of fish a week |
| Alpha-linolenic (ALA) | Flaxseed, walnuts | ~5–7 g/100 g flax | Partly converts to EPA/DHA |
How much food is needed to cover
- Vitamin D 2000 IU ≈ ~400 g of salmon a day — hard to get from food alone; sun/supplements are more effective.
- Omega-3 1 g/day ≈ ~100 g of fatty fish (one serving) a day, or 2 servings a week for prevention.
- ALA: 30 g of flaxseed gives ~1.5–2 g of ALA, but conversion to EPA/DHA is limited (~5–10%).
What is the VITAL trial?
The largest RCT (25,000+ people) from Harvard on the effects of vitamin D and Omega-3 on cancer and the heart.
What doses were used?
Vitamin D 2000 IU/day and Omega-3 (fish oil) 1 g/day.
Did vitamin D reduce cancer risk?
Not overall; but in the normal-weight subgroup (BMI<25) risk fell by ~25%.
Did vitamin D help with heart disease?
No, no significant reduction in cardiovascular events.
Did Omega-3 help against heart attack?
Not overall; but in non-regular fish eaters, infarction risk fell (~28%).
Should everyone take supplements?
Not everyone. Benefit is proven mainly with vitamin D deficiency or low fish intake.
What is the optimal vitamin D level?
Usually ~75–100 nmol/L (30–40 ng/mL) by the 25(OH)D test.
How much fish should I eat?
Two servings of fatty fish per week is recommended.
Do supplements replace medications?
No. VITAL confirmed that supplements do not replace treatment and lifestyle.
Where were the results published?
In the New England Journal of Medicine in late 2018.