Vitamins are not magical pills that will show results immediately after you start taking them. In fact, results are often subtle and slow to come by, so many fail to recognize they are getting better. Paying attention to changes in your body will help you understand whether the vitamins you are taking are working or whether you need to adjust the dosage or switch to a different brand or combination.
Make a list of any symptoms you have. These might include a lack of energy, dry skin, frequent colds or weak hair and nails. You can use a journal to keep track of what symptoms you are experiencing as you start taking your vitamins and note how serious the symptoms are, whether they change in intensity or remain steady and if new ones appear. As you start taking vitamins, note any improvements or changes you experience.
Note emotional and mood changes as well. For example, according to the website for the "Psychology Today" magazine, B vitamins are essential to fight off depression and maintain a good mood. They also seem to help ward off other mental health issues. The B vitamins also affect energy levels; if you notice a significant difference after taking the vitamins for a few weeks, you will know they are working.
Have your blood tested for iron and vitamin deficiencies. Your doctor can recommend a series of exams or estimate deficiencies, based on your symptoms. As you start taking your vitamins for that particular problem, note the changes that occur. Have another test made four to six months later to check that your numbers are up and that the deficiency is gone.
Look for external changes. If you have been trying to fix brittle hair or weak nails using cosmetic and beauty aids but have had no luck, the cause for the problem might be a vitamin deficiency. If your hair becomes softer and shinier, and your nails stop breaking regularly, this could be a good indication that your body is now obtaining enough vitamins to keep your body working--and looking--its best.