To Your Health

Q. Sometimes when I take my vitamins late at night I have trouble getting to sleep. Why is that and which ones are most likely to do this?

A. Insomnia after taking food supplements has been reported informally, but there is virtually no research on the observation. In fact, most of the research centers on the benefits of certain vitamins and minerals on sleep quality rather than sleep disturbance. Nevertheless, clinical experience indicates that some individuals do not sleep well when they take certain supplements late in the day.

The same supplements that have a reputation for increasing "pep" also seem to be the ones most likely to provoke some sleep problems. L-glutamine, one of the amino acids, can be converted in the brain into either GABA (gamma amino butyric acid) or glutamic acid. GABA is relaxing while glutamic acid is one of the most stimulating neurotransmitters. Most people tend to produce GABA from glutamine, and thus glutamine would help them sleep, but for someone who is prone to convert glutamine to glutamic acid, a glutamine supplement late in the day would actually interfere with sleep. This has been observed clinically but has not been researched.

Another amino acid that is a suspect for interfering with sleep is L-phenylalanine, the precursor of a family of neurotransmitters known as catecholamines. These substances are generally energizing, and their levels are highest in the morning, lowest at bedtime. Phenylalanine taken late in the day might artificially raise catecholamines when they should be diminishing in preparation for sleep.

B-vitamins that are ordinarily thought of as "energy boosters" might theoretically, if used at bedtime, boost energy too much. Any of the B-vitamins might fall into this category, but niacin has a distinctive property that is more likely to have an effect on sleep. A supplement of niacin above 100mg opens blood vessels and produces a flush in most people, an effect that is actually sought by many who suffer poor circulation. The flush can be mildly irritating and especially if it is unexpected it would be hard to sleep through.

Virtually all the minerals are above suspicion, more useful for improving sleep quality rather than hindering it. Calcium and magnesium have long been recognized as useful sleep aids, and zinc has recently been reported to treat a common sleep disorder in adolescents. Other minerals seem to have little effect, one way or the other, on sleep.

You might want to check your assortment of supplements to see if any contain an herb such as ephedra. Ephedra is a natural source of ephedrine, along with some other stimulating alkaloids, with chemical structures similar to amphetamine or "speed." Several herbs, which are not nutrients but commonly associated with them, are popular energy boosters and that certainly explains their tendency to induce insomnia.

A good night's rest is extremely important for optimum vitality, so if you suspect one of your supplements is disturbing your sleep, you should ferret it out and either change the timing of the supplement, reduce the amount used, or discontinue it entirely if necessary. Food supplements ordinarily do nothing but good, so if you find a downside to taking a nutritional supplement, you can probably do without it.