The other reply to your comment is entirely valid and I encourage you to read it in full. That said, the only way to measure a safe dose of a vitamin is to per

The other reply to your comment is entirely valid and I encourage you to read it in full. That said, the only way to measure a safe dose of a vitamin is to perform medical tests before and during a dosing regimen to ensure that you are neither under nor over the target levels of the vitamin in your body. Medical science is not yet reliable when it comes to defining target levels of vitamins in any individual's body. In general, for all body dosing regimens, the goal is to survive the dosing changes without dying first, and to produce the desired result second. If you are not treating a specific symptom and instead wish to simply calibrate your blood levels to "optimum", be warned: There is no optimum, period full stop. For example, if you increase your vitamin D levels precisely to a target amount with careful blood testing and supplement regimes, then your risk of death from sunlight exposure may increase if/when the levels of sunlight you're exposed to shift significantly (due to work, weather, or travel). Some will immediately object that the increase in risk is vanishingly small. You are irreplaceable. What level of risk of death of acceptable to you? Soylent calibrates their food product to 100% of all doses specified by the US RDA for healthy adults. It's generally assumed to be a safe set of targets, though some would say that it is too low in many respects (while missing the bigger picture of the 'pick one' conflict between society-level dosing and individual-specific dosing), and others would say that it is too high in many respects (while missing the bigger picture of the 'pick one' conflict between increased risk of side effects vs. increased risk of malnutrition). There's a good reason why everyone ends up at the same sentence, and I'm going to provide it now: Seek advice from a medical professional before consuming supplements. If you are unwilling to do so, get a med-alert bracelet and keep a summary of the past year of dosing changes in your wallet. It may someday save your life. If you are unwilling to wear a med-alert bracelet and keep a log of your self-alteration efforts, consciously accept that you risk death if unintended consequences occur.