In a recent study at Canada’s McMaster University, when subjects lost just 2 percent of the water stored in their tissues, their energy levels plunged 30 percent. Even mild dehydration makes it difficult for brain cells to communicate properly, plus it makes your blood volume and blood pressure dip, which slows the flow of oxygen and nutrients to your tissues, say Harvard researchers.
Common Tip-Off: Grogginess
Rx: Drink milk. Of course, drinking plain old tap water can help enormously -- sipping 12 ounces when they’re fatigued helps almost 100 percent of women feel more energetic within an hour, according to studies at Connecticut’s Manchester Memorial Hospital. But if you’ve been physically active, consider pouring a tall glass of milk (plain or chocolate) instead. “Milk rehydrates better than water because it replaces the sodium, calcium and other electrolytes lost in sweat -- and that’s key to quickly restoring your body’s fluid balance,” says Brian Timmons, Ph.D., lead researcher of the McMaster University study. “Plus it’s a great source of protein, so it can actually help prevent fatigue by keeping your blood sugar steady and your muscles well-nourished.”