Vitamin D Supplement Reference

I’m a big advocate of science-backed supplements to optimize mental and physical performance. These articles represent my own distilled research on effectiveness, risk, and other things to consider before supplementing. To see what supplements I am currently taking, definitely check out the “My Current Supplements” article at the top of this section. Most of the sources are dervived from, which is a great resource, but my intent is to distill it down and add my own research + anecdotes.

What is Vitamin D?

Vitamin D is recognized as one of 24 “essential vitamins” along with vitamins A, C, K, and B12, just to name a few. Fun fact - it is actually classified as a steroid that regulates the expression of close to 1000 genes in the body (124 of the genome), which makes it fairly important.

Vitamin D Sources

  • UVB Radiation (The Sun) - The body manufactures Vitamin D naturally when the skin makes contact with UV-B radiation from the sun. However, the amount of Vitamin D produced is marginal, and the risks of skin cancer from being exposed to UV-B radiation from natural sunlight offset any health gains from increased Vitamin D production1
  • Diet - Milk (124IU per cup) and fatty fish (500IU per salmon filet). Given the optimal levels of Vitamin D require 2000IU+ per day, the amount of Vitamin D needed from diet sources makes this a non-starter.
  • Supplementation

A report by the US Nutritional Health and Examination Survey in 20092 found that 75% of Americans are Vitamin D deficient. The survey naturally blames staying indoors, the use of sunscreen, and changing of American diets to the sharp increase in Vitamin D deficient adults. Plus we are discovering that biological optimal ranges of Vitamin D occur outside “historical normal” values, which means the medical guidance is showing most people are now deficient.

Benefits of Supplementation

Benefits are listed from best supported to least supported

  • Decrease in Overall Mortality - this may be a bit of correlation vs. causation issue, but the research does back an overall lower risk of death for non-deficient patients345
  • General Bone Health - Optimal Vitamin D levels, especially combined with Vitamin K supplementation, leads to stronger bones across all age ranges.6
  • Lower Blood Pressure - Linked study found an overall reduction of 5mmHg blood pressure when patients increased blood serum D levels.57
  • Higher Testosterone (in men) - A single study found raising Vitamin D serum levels also increased testosterone in men who were deficient.8
  • Higher estrogen (in women) - Single study found raising Vitamin D serum levels also increased estrogen in women who were deficient.9
  • Lower Cancer Risk - There is a strong correlation between Vitamin D deficiency and your risk of developing cancer. The following cancers have research backing this claim: breast cancer, colon cancer, prostate cancer, and pancreatic cancer. One study even claims that supplementation of 2000IU/day saw a 50% reduction of breast cancer incidence.1011
  • Increased Mental Performance - There is a linear relationship between Vitamin D levels and verbal fluency up to and exceeding 100ng/ml.12
  • Decreases Incidences of Depression - Low levels of serum Vitamin D (<20ng/ml) is highly correlated with incidences of depression. Fixing Vitamin D deficiencies has shown to be a solid first-line step in battling depression.13

Downsides and Toxicity to Vitamin D Supplementation

  • There is a risk of toxicity with taking too much Vitamin D. The reason behind this is around Vitamin D being a fat-soluable vitamin which can build up in the body over time. There are reported cases of over-supplementation leading to hospitalization. See the next section about how to not screw up the dosing for Vitamin D - thankfully most supplements are well within “safe” dosing ranges.

Now the fun part - toxicity! The National Institute of Health states that a consistent Vitamin D blood serum level of 200ng/ml is potentially toxic. The only way to get blood serum levels that high is to take 10,000-40,000IU supplements daily for close to three months. So yeah, super low to no toxicity, unless you are really trying. And fun fact - you cannot get Vitamin D toxicity naturally - food doesn’t have enough to get to those levels, and the skin regulates Vitamin D production automatically.14

Dosages and Timing For Vitamin D

The first step to figuring out if you need to supplement Vitamin D is to get a routine blood test to check for active Vitamin D levels. Your PCP can order this, or you can use a service like WellnessFX to self-service the blood test at a premium. Vitamin D production and absorption is impacted by several genetic markers, so there is no clear cut advice for everyone. When in doubt, the FDA recommends 1000IU-2000IU daily is safe for most of the population. Remember, you may need more or less given 1) how much Vitamin D is in your blood already and 2) your genetic markers for Vitamin D.

Once you have your blood test data back, you can compare your results against the table below. This table is roughly accurate with the most recent research on the topic of optimal Vitamin D blood serum levels.15

If your blood test comes back wildly deficient, then the highest safe dosage of Vitamin D is 10,000IU daily for three months. It is recommended to get your blood tested again and revise the dosing if necessary.

Timing wise, Vitamin D is best taken in the morning with a fatty breakfast. Taking Vitamin D at night can disrupt circadian rhythms16 and lead to poor sleep quality. If you don’t eat breakfast, then Vitamin D can be taken with Fish Oil to increase absorption. They also make Vitamin D capsules that have olive oil / other fats in them, which also can make a difference.

Gwern (an independent biohacker) also validated this timing evidence through his own experiment with taking Vitamin D at night.17

Vitamin D and Genetics

Your genetics play a large role in Vitamin D synthesis, usage, and storage. SNPedia keeps an up-to-date list of what genetic markers are known to positively or negatively impact Vitamin D levels - SNPedia Link. If you have done 23andme or genetic testing, then you can export that data in Promethease to check for these SNPs directly.


Since I’ve started tracking my own Vitamin D levels, I can say that I’ve never been clinically low in Vitamin D. I have always supplemented with 2000IU Vitamin D since college, so that has contributed to my relatively stable 60ng/ml blood levels. I have experimented with going up to 5000-10000IU daily with no success in impacting my blood levels, but that may be due to genetic and other health factors. I want to try and get closer to 75ng/ml overall, since that is the current guideline for long term bone and heart health.


Conclusion and Recommendations

You should take 2000IU or more Vitamin D daily. There is virtually no downside and it costs about $0.06 a day to do it.

Recommended Brand: Nutrigold 2000IU. This brand has a great score on LabDoor in regards to quality. Link to LabDoor Vitamin D Page

Vitamin D is extremely cheap to supplement. High quality 5000IU capsules cost about $0.06 per day on average, which is a cheap price to pay for a staple nutritional supplement.

Research / Sources