Daily Melatonin Levels in Women with Systemic Lupus Erythematosus

Dear Editor,

Sir, in a recent issue of Balkan Medical Journal, we have read with a great interest the published article by Robeva et al. (1) entitled “Decreased daily melatonin levels in women with systemic lupus erythematosus - a short report”. The authors showed that daily melatonin levels were decreased in women with systemic lupus erythematosus (SLE). However, we think that some points should be discussed.

Melatonin is a hormone that found in plants, animals and microorganisms. Melatonin is mainly produced and secreted by pineal gland in humans. Secretion occurs in dark, and peaks at 2 to 4 a.m. (2). Its production is suppressed by exposure of light to retina. It is especially blue light, at a wavelength of around 460 to 480 nm, which inhibits melatonin secretion in the morning. 90% of the hormone is cleared from circulation in one passage through the liver after secretion. Because of these causes, serum samples obtained at after dawn are not suitable for evaluating melatonin levels. 6-hydroxymelatonin sulphate (6-HMS) is the major hepatic metabolite of melatonin and is primarily excreted in the urine. It has been accepted that urine 6-HMS is a good biomarker of pineal gland activity for desired period (3).

Several kinds of plants contain considerable amount of melatonin such as banana, orange and pineapple. Therefore, consuming such foods give rise to significant increment on serum melatonin levels (4). In this study, the authors did not define the eating habits of participants in terms of above plants. In addition, for the control group, psychiatric disorders, medication (e.g. β-blockers), and metabolic disorders should be expressed in detail.

The authors have stated that the mean age was not significantly different between the two groups. However, they compared three groups: short photoperiod SLE, long photoperiod SLE and control groups. It is known that melatonin production clearly declines with age (2). In this regard, the mean ages of three groups should be defined clearly, to assess whether there were differences and to prevent misunderstanding.

The diagnosis of SLE is based on a combination of clinical findings and laboratory evidence which have been defined by the American College of Rheumatology (ACR). The ACR recommends antinuclear antibody (ANA) testing in patients with two or more unexplained signs or symptoms of SLE. According to the Evidence-Based Guidelines for the use of ANA testing, the average sensitivity of the ANA was 93% and the specificity was 57% for the diagnosis of SLE (5). In this regard, the rate of ANA positivity in patients with SLE in this study, which was 71%, is questionable.

In conclusion, as we believe that this study contributes valuable information to the literature, an explanation of above concerns will certainly present reliable data to the readers.