22 years old f. lost 7kg in 6 months. no gym no dieting. but i walk 4km a day and used to walk 3 earlier. is this cause for concern? no other symptoms

Diet/exercise: are the mainstays of weight loss and good cardiac health. Portion control is a valid alternative to losing weight. I would not be overly concerned, unless you have symptoms.

If continues: I would not be concerned unless to continue to loss a lot of weight if nothing new.Keep regular checkups with your doc

Agree with Dr. M.: Keep track of your BMI so that it does not go below 18.5 : Link for BMI calculator: https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm Have a healthy diet, exercise 30 minutes/day, drink plenty of water, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV vaccine