Obviously, a lack of vitamins will take its toll eventually but what vitamins and herbs provide most is vitality. There is a difference. You can get energy from amphetamines or caffeine and even if you are run down you may stay awake and get a lot done, but beneath this veneer of energy the body doesn't feel right. With vitality, even if the body is tired from hard work, it feels good beneath it all and simple sleep restores and refreshes it. Our ancestors who lived in days with no labor saving devices worked incredibly hard from sunrise to sunset.
Vitality is a summation of good nutrition, enough rest and exercise.
A body that doesn't get exercise spirals down. The less you do the less you want to do. The less you want to do the less energy reserves you have for simply getting through the day. Sleep is restorative and some people who lack energy may not be getting enough sleep. Sleep apnea, for example, is an inability to breathe while asleep.