People over the age of 65 are more likely to suffer heat stress and illness than younger people. For example, during the decade from 1999-2009, approximately 40% of all heat-related deaths were adults over the age of 65.
The reason that older adults are more susceptible is because, when exposed to heat, older people are not able to generate blood flow to the skin as effectively as younger people, making them more prone to cardiovascular events, such as heart attack or stroke.
Normally, during hot weather or exercise, the body increases blood flow to the skin, which in addition to sweating, helps to cool the body and regulate temperature. In older adults, this process becomes less efficient, as aging blood vessels produce less nitric oxide, and cannot dilate properly. Nitric oxide signals the smooth muscle surrounding veins, arteries and lymphatic system to relax, therefore increasing blood flow.
This increase in blood flow, also known as vasodilation, results in more blood flow to the skin, which allows the heat of the blood to be released more easily. This is an important mechanism for allowing the body to regulate its core temperature, when exposed to heat. The opposite action occurs when exposed to cold, in order to keep the body warm.
Research from Pennsylvania State University, funded by the National Institutes of Health, suggests that supplementing with folic acid may be an inexpensive but effective way to help older people weather heat waves, by increasing nitric oxide production, and consequently, blood flow to the skin.
The study, titled “Folic acid supplementation improves microvascular function in older adults through nitric oxide-dependent mechanisms”, published in the Journal Clinical Science, involved 11 healthy older adults (average age 71), and 11 healthy younger adults (average age 22), in two sub-studies.
Production of nitric oxide by the blood vessels is dependent on an enzyme that needs cofactor tetrahydrobiopterin, also known as sapropterin, or BH4. Bioavailability of this vital cofactor, which is also involved in the synthesis of serotonin and melatonin, decreases with age.
Previous research revealed that supplementation with BH4 increased production of nitric oxide in older adults, and since folic acid increases bioavailability of BH4, researchers hypothesized that supplementation of folic acid would result in increased nitric oxide production.
To test this hypothesis, they conducted two sub-studies in healthy adults without cardiovascular disease, in order to isolate the effect of age. One sub-study involved localized heating, and the other involved whole-body heating.
In the localized heating sub-study, folic acid or placebo was delivered locally to the blood vessels via intradermal microdialysis fibers, at randomized sites on their arms. Researchers found that blood vessels which received folic acid produced more nitric oxide than those at the control sites.
In the whole-body sub-study, participants took either 5mg of folic acid supplement or placebo daily for six weeks. In this group, older subjects who received folic acid had improved cutaneous vasodilation, but not younger subjects.
Previous studies on increasing nitric oxide production, and subsequently, blood flow to the skin had used expensive pharmaceutical products, but this work suggests that the less expensive option of folic acid supplementation may offer benefits for the elderly.
Researchers noted that future research should focus on whether folic acid could improve blood vessel function in people with cardiovascular disease, as well as potential links between life-long supplementation and cardiovascular health.