As we all know, age, gender, sex hormones, osteoporosis, hypertension, hyperlipidemia, diabetes and hyperuricemia are all considered as risk factors of BPPV (6–9). According to previous study that cerebrovascular risk factors influenced BPPV recurrence(10). The morbidity of BPPV in male and female is 1:1.5-2, which is usually high after 40 years old and increases with age (4). In addition, some studies have found that age does not increase the recurrence rate of BPPV (10).We found the recurrence of females was 3.79 fold which significantly higher than male but the female -to-male ratio was 1.82 to 1 in total patients. In theory, with the increase of age, the function of human organs gradually decline. As a part of inner ear structure, the metabolism, absorption and regeneration of otoliths are affected, and can easily fall off and leading to the recurrence of BPPV. Previous studies have found that the high morbidity of BPPV in female may be related to widespread osteoporosis(5). It may also be related to the abnormal hormone metabolism in postmenopausal females. But we found there is none correlation with the common BPPV related risk factors in the observation group, reasons for the small number of cases cannot be excluded.
However, our research showed that the recurrence patients of BPPV was very higher than the same period under the quarantine policy in Hangzhou from January 2020 to March 2020. This maybe correlated with their unhealthy lifestyle during COVID-19 spread.
In the life style of BPPV patients in the observation group, the majority of patients has the following characteristics, such as poor physical activities, and prolonged recumbent position time. Especially after implementing the policy on February 4, 2020. It can be seen that prolonged recumbent position time, lack of exercise may be the important pathogenic factors of BPPV recurrence. Van WE had confirmed that 11% of the dizziness symptoms in Parkinson's patients are likely to have BPPV, which is also considered to be related to exercise reduction (11). It has been suggested that prolonged bed rest may promote calcium carbonate deposition and otolith relaxation in the elliptical capsule (7). The author believes that this viewpoint can better explain the mechanism of the significant increase of BPPV patients in our study. Studies have found that lack of exercise is one of the most important risk factors for BPPV recurrence. Morbidity of female who do not exercise is 2.62-fold that of regular exercise (12). Regular physical exercise may be a good choice that reduces the risk of BPPV recurrence.
Some studies found that the decrease in the plasma vitamin D level is directly related to the occurrence and recurrence of BPPV (13, 14). However, contrary to these finds are other studies which have found that seasonal vitamin D deficiency in winter is not enough to cause BPPV (15). The quarantine policy allowed one person per household family to leave the apartment to undertake supplies shopping once every two days for a period of one hour in Hangzhou. This is for gathering supplies and as such very little skin is exposed to the sunshine, and this may be result in vitamin D deficiency. However, it is regrettable that the plasma vitamin D of these patients had not been determined. Our study also showed that sun time was not associated with BPPV recurrence
The authors suggest that BPPV may not be caused by the falling off of otoliths in the utricle into the semicircular canal. It may be the change of the composition of the endolymph or the deposition of the inherent composition. We proposed the "sediment" theory of BPPV. This kind of deposition is easy to deposit in the posterior or horizontal semicircular canals due to the gravity effect when lying for a long time, but not in the anterior semicircular canals. The deposition of sediments in healthy people may be continuous, which may be absorbed and dissipated due to regular exercise and suitable recumbent position time. For those who lack exercise and prolonged recumbent position time, sediments deposition is affected by gravity, and when they move position such as getting up from a resting position or turning over this causes sediment displacement which then results in BPPV. This finding may explain why BPPV occurs several days after trauma, rather than immediately after trauma.