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IU are used whenever a particular vitamin has multiple forms with varying levels of efficacy [0]. Or it may be used when the typical quantities are measured in inconveniently small units.

1 IU of cholecalciferol is 0.025 micrograms. If you supplement vitamin D at hogh doses, make sure you use cholecalciferol rather than ergocalciferol. The former is naturally synthesized in your own skin, whereas the latter is produced mainly in mushrooms, and can result in unpleasant side effects. Maximum-dose recommendations from nutritionists may include the assumption that the consumer does not know the difference, therefore reflect the highest safe dose of the least-safe vitamer.

It is similar to the issues with vitamin A, when someone may safely supplement with carotenes and unsafely supplement with retinol. You can eat sweet potato and carrots until you turn orange, but you cannot eat a single bite of polar bear liver. But because we are mostly idiots, nutritionists cannot recommend a high-dose supplement for vitamin A, with carotene in mind, because someone will inevitably overdose themselves with retinol. So if you can certify yourself as not-a-moron, you will be able to figure out when those recommendations may be safely ignored.

[0] https://en.wikipedia.org/wiki/Vitamer




Where can one go to learn about different forms of vitamins and the safe&recommended doses for each?


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.


Unfortunately, most of the sites that claim to aggregate such information are heavily incentivized to misrepresent or falsify information in order to sell you supplements, either directly sourced or through affiliate programs.

Many of the remainder are constrained by politics or medical malpractice law. For instance, USRDA recommendations and USDA gimmicks like the food pyramid are heavily influenced by agricultural businesses. Minimum daily requirements are mostly based on the amounts needed to avoid showing symptoms of known deficiency diseases, rather than to actually be healthy.

The actual scientific research is rather sparse. I am aware of a study performed in the 1960s that completely replaced all meals with a nutrient slurry with the texture of corn syrup, which was partially spoiled because subjects were convincing accomplices to smuggle real food to them. Thanks to subject compliance issues, most long-term research is done on analysis of food-diary observations and surveys. Short-term research, such as for satiety and glycemic response, is more controllable.

You will have to do a lot of your own digging.

Start with professional athletes like swimmers, cyclists, and bodybuilders, but beware the "broscience". Look at the life extension people that use caloric restriction and intermittent fasting. Check out the Soylent people. Look at the practice of geophagy. Listen to some vegans. Study some biochemistry, especially the Krebs cycle and the known DNA repair and disease-fighting mechanisms. Do a lot of Wikipedia walks.

Be aware that your nutrient requirements will vary from others as a result of your personal genetic quirks, but mostly can be expressed as a ratio of mass to ingested kcal.

Learning the biochemistry is key. You have to know that omega-3 and omega-6 fatty acids use some of the same enzymes at particular steps in their metabolic chains, so those fats will compete with one another in your body, meaning that those nutrients must be in a balanced ratio to each other, regardless of your absolute consumption. What's the best ratio? I don't know. Cursory analysis suggests that 6 parts omega-6 to 1 part omega-3 is too high. Supplementing with krill oil, algae oil, chia seed, or flax meal would therefore be as warranted as cutting the amount of omega-6 from vegetable oils.

If you look at Na+/K+-ATPase, it actively transports sodium and potassium across the cell wall until the interior is mostly K and the exterior is mostly Na. Your dietary requirements are likely related to the homeostasis mechanisms for regulating the ionic concentrations. What's the best ratio? I don't know. Cursory analysis suggests that your body requires overall 2.25 times as much K+ as Na+ at any given time, but the K+ is more strongly conserved, being mainly inside your cells. So you should probably eat a ratio similar to that found in your extracellular fluid, which is 33.5:1 Na+:K+, which indicates that your table salt should probably be at least 1:24 KCl:NaCl by mass. Sea salt provides some K, but not that much--about 1:200. And it also shouldn't be more than 3:1 KCl:NaCl by mass, even if you are severely deficient, because your body needs the Na+ to be present to pump K+ into the cells.

It's all guessing, and the signal-to-noise ratio is very low.




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