Studies show than vegans in general have lower B12 levels than non-vegans, but according to this article, 'nearly 40% of the U.S. population may be flirting with marginal vitamin B12 status'. This study also found that in a group who consumed fish, poultry or red meat on a regular basis, 40 per cent had vitamin B12 concentrations below the recommended lower limit.
A study of elderly people in Italy (90-106 years old!), although appearing well-nourished, had deficiencies in a number of micronutrients, such as selenium, zinc, vitamin B6, Vitamin E, vitamin B12, and folate.
Other studies show that many are short of recommended levels for certain nutrients such as calcium, iron, zinc, and folacin, some are short in vitamins A and C (based on 'normal' people, not vegans).
According to this link, 34% of all meat eaters are B12 deficient, and most Americans are not getting what they need from their diet: "For example, in one recent U.S. Dept. of Agriculture survey of 20,000 people, not a single person was consuming adequate levels of all the vitamins and minerals. In this study, the percentage of Americans were found to be deficient as follows: 90% in vit. B6, 75% in magnesium, 68% in calcium, 57% in iron, 50% in vitamin A, 45% in vitamin B1, 41% in vitamin C, 34% in vitamin B2..." and the list goes on.
According to this study, "The matched subjects who ate meat (including poultry and fish) were more than twice as likely to become demented as their vegetarian counterparts".
In a study of 402 elderly Europeans living at home, the nutrient content of their diet was found to be low: folic acid intake was low in 100% of those studied, zinc in 87%, vitamin B6 in 83%, and vitamin D in 62%.
Here's a list of nutrient common deficiencies (again, not based on vegans) from the Hippocrates Institute, Volume 22, Issue 1: 80% are vitamin B6 deficient. 75% are magnesium deficient. 68% are calcium deficient. 57% are iron deficient. 50% are a deficient. 45% are B1 deficient. 41% are Vitamin C deficient. 34% are B12 deficient. And the list goes on like that.
(Maybe be that the definition of 'deficient' needs to be re-evaluated, or that 'low levels' are mixed up with 'deficient'?)
To quote on of the sources listed above, there are 'literally hundreds of medical studies to suggest it’s a virtual certainty that you and every member of your family are deficient in one or more essential nutrients' (addressed to 'normal' people, not vegans.)
Still, it seems that some people think that they need to be more concerned about nutrient deficiencies as vegans than they needed to be before they became vegans.
We already have a thread about this topic (here), but this time I'm posting a poll: Do you believe that vegans generally need to worry more about nutrient deficiencies/health than they did before they excluded animal products from their diet?