What vitamin D level should an APOE4 carrier aim for?

The vitamin D bands

The optimal band includes both ends: 30.0 and 50.0 are optimal, and 50.1 is above target. The above-target band includes 100, so 100.0 is above target and 100.1 is the line to talk to your doctor. "Under 20" excludes 20, so 20.0 is below target.

To convert, multiply ng/mL by 2.5 to get nmol/L (NIH Office of Dietary Supplements). 40 ng/mL is 100 nmol/L.

Confidence in the optimal band: moderate. The floor is backed by dementia data and the ceiling by the NIH. The exact 30 line is a Phoenix choice.

Why does vitamin D matter for your brain?

Low vitamin D raises dementia risk, and a genetic study says the low level itself is part of the cause. Extra vitamin D on top of enough does nothing for the brain.

• Deficiency and dementia. In 1,658 older Americans followed for 5.6 years, people under 10 ng/mL (25 nmol/L) had a dementia hazard ratio of 2.25, and people at 10 to under 20 ng/mL had 1.53, against people at 20 or more. Risk rose sharply below 20 ng/mL (Littlejohns, 2014).
• A genetic test of cause. In the UK Biobank, a Mendelian randomization analysis, which uses genes to rule out lifestyle confounding, found dementia risk 54% higher at 10 ng/mL (25 nmol/L) than at 20 ng/mL (50 nmol/L). The authors estimated that raising everyone to at least 20 ng/mL could prevent 17% of dementia. Brain volumes were lower at both low and high levels (Navale, 2022).
• Trials in people who already had enough. Three large trials gave vitamin D to mostly replete older adults and found no brain benefit: VITAL at 2,000 IU a day (Kang, 2021), D-Health (Pham, 2023) and the Finnish Vitamin D Trial (Lönnroos, 2025).

The pattern is clear: fix a low level, and do not chase a high one.

What does APOE4 change?

APOE4 does not need a different vitamin D number, and carriers tend to run a little higher.

• APOE4 went with higher vitamin D levels in mice and in a population sample of 699 people (Huebbe, 2011).
• In 12,388 people from US Alzheimer's centers, those who took vitamin D supplements had 40% fewer new dementia cases than those who did not (hazard ratio 0.60). The difference was smaller in APOE4 carriers than in non-carriers (Ghahremani, 2023). This was an observational study of people who chose to take supplements.

Phoenix uses one band for every carrier. A 3/4 against 4/4 split has no study behind it.

What did Phoenix choose, and why not higher?

I chose 30 to 50 ng/mL for Phoenix after weighing three facts.

• The floor. Dementia risk climbs below 20 ng/mL (Littlejohns, 2014; Navale, 2022). Phoenix sets its floor at 30 to keep a margin above that. This is a Phoenix choice: in 2024 the Endocrine Society stopped endorsing its old definition of "sufficiency" at 30 ng/mL (McCartney, 2024).
• The ceiling. The NIH links levels above 50 ng/mL to potential adverse effects, particularly above 60 (NIH Office of Dietary Supplements, 2025).
• The middle ground. Between 50 and 100, Phoenix shows "above target" and does not lower your score. No trial shows a brain gain from going higher.

Some clinicians and posts suggest 50 to 80 or 40 to 70 ng/mL for carriers. Those ranges sit above the NIH caution line, with no carrier evidence behind them.

What moves vitamin D?

Here are the levers, ranked by how much they move your level. These are facts, not a dose for you: the right amount depends on your result, your weight and your doctor.

1. Daily vitamin D3 dose: about 5 to 7 ng/mL per 1,000 IU a day at usual doses. In 17,614 adults, each 1,000 IU a day raised 25(OH)D by about 12 nmol/L (about 5 ng/mL) in the 0 to 1,000 IU range. The rise flattened at high doses, to about 1 nmol/L per 1,000 IU between 15,000 and 20,000 IU a day (Ekwaru, 2014). In a controlled winter trial, each extra 40 IU raised the steady level by about 0.7 nmol/L, or about 7 ng/mL per 1,000 IU (Heaney, 2003).
2. Body weight: people with obesity ran about 8 ng/mL lower. On the same intake, people with obesity averaged 19.8 nmol/L (about 8 ng/mL) lower and people with overweight 8.0 nmol/L (about 3 ng/mL) lower. The authors estimated that people with obesity need 2 to 3 times the dose to reach the same level (Ekwaru, 2014).
3. Sun and season. Healthy men in a winter trial were using an estimated 3,000 to 5,000 IU a day and met over 80% of their winter need from stores built by summer sun (Heaney, 2003).
4. D3, taken daily. D3 raised 25(OH)D more than D2, mainly in large occasional doses (Tripkovic, 2012). For people over 50 who need vitamin D, the Endocrine Society suggests daily doses over intermittent high ones (Demay, 2024).

The safety side: the NIH's adult upper limit is 4,000 IU a day (NIH Office of Dietary Supplements, 2025). In a 3-year trial, mild, passing high blood calcium appeared in 0% of people on 400 IU a day, 3% on 4,000 IU and 9% on 10,000 IU (Billington, 2020).

What Phoenix members use: among Phoenix members who log their supplements, 174 have logged vitamin D3, and 169 log it as taking now (2 October 2026).

How often should you retest?

The Endocrine Society suggests against routine vitamin D testing in healthy people, because no trial shows that testing helps (Demay, 2024). Phoenix tracks it anyway: you want to know whether your dose put you in range, and not far above it.

Vitamin D in the blood has a half-life of about 15 days (NIH Office of Dietary Supplements, 2025), so a new dose takes a couple of months to settle.

Phoenix practice: if your result is outside 30 to 50 or you change your dose, retest about three months later. Once you are in range, keep vitamin D in your regular panel.

In practice, the 70 Phoenix members who uploaded two or more vitamin D results waited a median of 315 days between their first and latest test.

What Phoenix members' results show

Start with the whole group. 157 Phoenix members who uploaded their results have a vitamin D test on file (2 October 2026; 93 carry 4/4 and 48 carry 3/4). Their median latest result is 54.4 ng/mL: above the Phoenix target.

The rest, fewer than 10 members, sit under 20 or above 100.

Among carriers at Phoenix, the problem is not too little vitamin D. It is too much: more than half sit above 50 ng/mL, where going higher brings no benefit.

70 members have tested twice or more, a median of 315 days apart. Their median moved from 53.5 to 56.9 ng/mL. Of the 46 who started outside the 30 to 50 band, fewer than 10 ended inside it.

In Phoenix's first research release (476 paying members), 23 of 58 repeat testers improved their vitamin D, 12 held steady and 23 got worse.

Three of three members who started vitamin D3 in that release raised their level: an APOE4/4 woman in her 60s from 28 to 102 ng/mL in 126 days (+264%), an APOE2/4 woman in her 50s from 32 to 66 in 69 days (+106%), and an APOE4/4 man in his 50s from 33 to 54 in 120 days (+64%). Each took D3 as part of a combination: with Lysoveta (a DHA supplement) for the first, with omega-3 for the other two. D3 works. All three also overshot the 30 to 50 band, and the first crossed 100, the line to talk to your doctor.

Members chose their own supplements and doses, and many changed more than one thing at a time. Every figure here is an anonymous aggregate or a de-identified case.

When should you talk to your doctor?

Talk to your doctor if your vitamin D is under 20 ng/mL (50 nmol/L) or above 100 ng/mL (250 nmol/L).

• Under 20 is below the level that meets the needs of 97.5% of people (Ross, 2011). A doctor can look for the cause and choose the right treatment.
• Above 100, review your supplement intake and your calcium with your doctor. Symptoms or an abnormal calcium result make it more pressing.

Between 50 and 100, nothing is urgent. If your doctor prescribed a vitamin D dose, do not change it because of this page.