ecelizzy asked
Why do B-vitamin supplements sometimes have 1,000%, or more, of their RDA? Isn't 100% enough? Does it have to do with absorption? And if so, shouldn't that be considered in determining RDA?
Answer
It is important to understand what RDA (Recommended Dietary Allowance) means. By definition, the RDA is the "daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people." In other words, the RDA is the amount of a certain vitamin, mineral etc... that is needed to prevent disease, bodily function breakdown etc... It has nothing to do with the potential benefit supplementation can provide.
For example, Niacin (vitamin B-3) is a popular supplement used to increase HDL (i.e "health cholesterol") levels. The RDA is 16 mg per day to prevent disease (e.g. pellagra). However, many studies indicate that Niacin needs to be supplemented at doses of 500 mg or higher to benefit blood cholesterol numbers.
B-Vitamins Supplementation Vs. Recommended Daily Allowance
B-vitamin are often added in copious amounts (much higher than the RDA) to a variety of products including:
- Energy Drinks
- Multivitamins
- Energy supplements
- Foods
To demonstrate, below is a label for Nature's Way B-50 complex:
A variety of B-vitamins (e.g. B1, B3, B6 and B12) are thought to confer benefit when supplemented. Most often, B-vitamins are thought to reduce stress or decrease anxiety but are also theorized to reduce cardiovascular disease...among other problems. There is some truth to B-vitamins being beneficial when used in amounts over the RDA. For example, vitamin B6 (pyridoxine) has some evidence that it can reduce neuropathic pain in diabetics.
In addition, studies show certain elderly individuals may need, and benefit from, extra vitamin B-12 to avoid developing anemia as the ability to absorb the vitamin can significantly decrease with age. These people often experience improved energy with B12 supplements but the benefits generally occur only if they were deficient to start with.
Safety Of Exceeding RDA Of B-Vitamins
B-vitamin supplementation is often thought safe as they are "water soluble" vitamins. Doses in excess of what the body can absorb are simply eliminated in the urine. This is why often times, after taking large doses of vitamins, the urine is a bright orange/yellow color.
However, recent data suggests that there are individuals that are affected when they ingest too high doses of B-vitamins. For one example, ingesting too much B6 chronically can lead to neuropathy (which is interesting as B-6 use has been investigated to treat neuropathy as well).
Nevertheless, it is generally accepted that B-vitamins are safe to take, even in doses that exceed the RDA. There may be issues when taking extremely high doses chronically, but serious problems would be unlikely.
Summary
To summarize, B-vitamin supplementation above the recommended dietary allowance is common and is generally regarded as safe. Supplements with certain B vitamins have been shown in studies to confer certain benefits including:
- Reduction of anemia
- Lessened cardiovascular risk
- Improved energy
- Decreased neuropathic pain
In addition, as B-vitamins are mostly water soluble, the majority of doses that are not absorbed are simply eliminated via the urine. However, there is still a good deal we don't know and excess B-vitamin intake has been associated with certain negative consequences, although these appear to be relatively uncommon.
