The UAE has one of the sunniest climates on earth and some of the most widespread vitamin D deficiency anywhere, because from May to October most residents live between an air-conditioned flat, an air-conditioned car and an air-conditioned office. Levels tend to bottom out in early autumn, after a summer spent entirely indoors — the opposite of what most people assume. Hydration is the other big seasonal variable: mild dehydration in a Gulf summer concentrates your blood, which can nudge haemoglobin, creatinine and electrolyte readings upward even when nothing is wrong.
The calendar matters in softer ways too. Shamal winds lift fine dust in late spring and early summer and set off a wave of sneezing that gets blamed, often wrongly, on food. Winter is the UAE's outdoor season, when runners and cyclists suddenly care about ferritin and iron. Ramadan moves the entire country onto a fasting schedule that happens to be ideal for certain tests and unhelpful for others. A home collection service lets you work with these rhythms instead of around a clinic's opening hours, which is most of the reason the category exists.