You might get nervous during take-offs and landings (breathe deeply). And, sure, sometimes the in-flight food options are enough to make you nauseous (pack your own snacks). But the 3 major health issues for air travelers are a little more complicated. Heres what they are and how to avoid them.

1. Jet Lag

The culprit: Crossing several time zones can drape precious vacation days in grogginess.

Before you fly: If youre flying east across several time zones, book an early flight. Flying west, book a later flight. Also, eat a high-protein breakfast on travel days to hike alertness.

In the air: Set your watch on destination time. And avoid dehydration (which increases jet-lag symptoms) by drinking plenty of water.

At your destination: Get outside for a burst of melatonin-suppressing natural light (to keep you awake). If youve flown east overnight, walk in the a.m. If west, get outdoors in the afternoon. If you must, nap for 20 minutes to take the edge off your fatigue. Eat a high-carb dinner on arrival night to increase sleep-inducing serotonin and melatonin. And at bed-time, if youre having trouble sleeping, a dose of melatonin (0.5 to 5 milligrams) can help.

2. Dehydration

The culprit: Blame airplane air and its lack of humidity (about 15 percent).

Before you fly: After going through security, buy a bottle of water, even for short flights.

In the air: Skip alcohol and caffeine; they hasten dehydration. And shoot for 8 ounces of water for every hour youre in the air.

At your destination: Drink more water!

3. Deep Vein Thrombosis (DVT)

The culprit: When you sit too long, particularly in an airplane where the air pressure is reduced, blood may pool in major deep-leg veins, leading to clots that can break off and cause life-threatening pulmonary embolism (PE) and, in very rare cases, stroke.

Before you fly: If youve had DVT or PE, have had recent surgery, are pregnant or are taking hormone-replacement therapy, or have a malignancy or blood-clotting abnormalities, talk to your doc. During long flights you may need to take blood-thinning medications (such as heparin) or wear compression stockings or support hose to reduce leg swelling.

In the air: Get your blood moving with a walk down the aisle. Or try this: Extend your legs and flex your ankles, pulling up and spreading your toes. Then, push down and curl your toes; repeat 5 times.

At your destination: Get out and walk! And keep an eye out for symptoms of unusual leg discomfort or shortness of breath—blood clots can start to show symptoms as long as several weeks after a flight.