Vitamins become toxic when they are taken in large amounts and not released from your system. With that said, Iron and Calcium are usually the vitamins that can quickly build up. As long as you are flushing the vitamins out of yoru system each day, and stay within the daily intake limit for you, you are OK.
I think if you're concerned medically, you should really discuss it with a licensed doctor/medical practitioner. They will know what your specific daily limit for certain vitamins may be (could be higher or lower than the generic postings) and could provide more background information thatn those of us not licensed in the study of medicine -- such as myself
).
With that said...
I just googled a few articles that were interesting to me when I was taking multiple supplements a few years back -- Not meant to scare you, but rather just provide insights and things to avoid/remain cognizant of as you continue in your journey of good health.
Hope this helps, and good luck!
Warm Regards & Signing Off,
Lovie
"As with most substances, it is the amount consumed that is the key. Almost anything is toxic if consumed in excess, including salt, alcohol and even water or oxygen! Provided that supplements are taken in the amounts recommended on the pack by the manufacturer or retailer, and the recommended doses are not exceeded by combining too many different supplements, then it is highly unlikely that supplements will cause toxicity.
Water soluble vitamins - such as the B group vitamins and vitamin C - cannot be stored by the body to any great extent, so if you take in more than your body needs, they are simply excreted. However, the fat soluble vitamins A and D can accumulate in the body, but pose no danger to your health if consumed within the safe upper limits indicated for them. The exception is in pregnancy, when large amounts of vitamin A may pose a risk to the developing infant.
Combining supplements will not normally interfere with the way they work and in some cases may be beneficial. However, certain supplements may interact with each other, for example, there is competition within the gut for the absorption of different minerals and a large dose of one might decrease the absorption of another or cause excessive absorption of another. Generally speaking though, this is not a problem. Take vitamin D and calcium for instance. No matter how much calcium you take, it will not be anywhere as beneficial as if you took a moderate amount of both vitamin D and calcium together.
Therefore a high quality liquid multivitamin and/or mineral product is best for all-round supplementation because it delivers nutrients in the right balance. Before combining supplements, people should consult their doctor, pharmacist or the company manufacturing the supplements for advice, or simply stick to a high quality multi that has most of what you need and simply add the additional nutrients you seek for your own specific needs.
As our bodies age, they become less efficient at absorbing some of the nutrients from our diet making it important to ensure that the right quantities of relevant vitamins and minerals are consumed. For example, as we get older our bodies are less able to absorb iron but Vitamin C can help increase absorption, as can multivitamins in liquid form. On the other hand, we are also more prone to toxicity as even water-soluble vitamins are not excreted as much because of our less efficient kidneys. Individual sensitivities and variations in response can occur, so if any unexpected symptoms appear whilst taking a particular supplement, medical advice should be sought."
Source:
http://www.vitamins-nutrition.org/vitamins/vitamin-overdose.html
Additional Reading:
[Edit: Added 1 More Link]
Vitamin Toxicity
http://www.healthatoz.com/healthato...RI=/healthatoz/Atoz/ency/vitamin_toxicity.jsp
Multiple Vitamin Overdose
http://www.nlm.nih.gov/MEDLINEPLUS/ency/article/002596.htm#Poisonous Ingredient
Time Article: Vitamin Overdose
http://www.time.com/time/magazine/article/0,9171,996706,00.html
Dietary Reference Intake - Our Daily Dosage Limit for Vitamins
http://en.wikipedia.org/wiki/Dietary_Reference_Intake#Vitamins_and_minerals
Vitamin Poisoning
http://en.wikipedia.org/wiki/Vitamin_poisoning