In this 7-month randomized controlled trial, children aged 1-6 years with asthma attacks triggered mostly by colds, will receive a high dose of vitamin D or a placebo every 3.5 months during their usual clinic visit. This study will test whether children receiving a high dose of vitamin D have less frequent and less severe asthma exacerbations compared with those receiving placebo.The study will also document the safety profile of this strategy.