Are ‘can’ and ‘or’ correctly used in the first sentence? What about ‘between’ and ‘help’ in the last sentence?

Are ‘can’ and ‘or’ correctly used in the first sentence? What about ‘between’ and ‘help’ in the last sentence?

Sleep deprivation can lead to reduced brain function, fatigue, headaches, and weight loss or gain. You need between seven and nine hours of sleep to help improve you overall health.