A review of 67 studies involving 230000+ people found that the vitamin supplements mayn't cut risk of dying. Even more, some supplements may increase mortality.
The study examines effect of Vitamin A, Vitamin C, Vitamin E and selenium intake with varying doses.

The study found that Vitamin A, Vitamin E and beta-carotene increases death risk. Vitamin C and selenium seem to not affect death risk.
Also Vitamin C is reported to not increase longevity.

Children who get vitamin D have a lower risk of type 1 diabetes.

Researchers combined data from public studies and suggest that vitamin D supplements cuts child risk of type 1 diabetes by 29%.

It's not clear how vitamin D might fight diabetes. However, Zipitis and Akobeng note that insulin-making beta cells in the pancreas are sensitive to vitamin D.

(More: http://diabetes.webmd.com/news/20080312/vitamin-d-may-cut-child-diabetes-risk)

Researchers: High doses of vitamin E linked to higher risk of lung cancer.

The study of 77000 people: long-term taking 400 mg/day increased lung cancer risk by 28%. Taking beta-carotete can lead same risk.

... Vitamin E is known to be an antioxidant - protecting cells from molecules called free radicals.

But the US researchers speculate that, in high doses, it may also act as a pro-oxidant - causing oxidation and therefore damage to cells. ...

Six-year vitamin E supplementation increased tuberculosis risk by 72% in male smokers who had high dietary vitamin C intake, but vitamin E had no effect on those who had low dietary vitamin C intake, according to a study published in the British Journal of Nutrition.

(Source: http://www.sciencedaily.com/releases/2008/02/080221101425.htm)

Vitamin E and ?-carotene affect the immune function and might influence the predisposition of man to infections.

Elderly people deficient in a key type of vitamin B could have a three times higher chance of developing dementia, researchers say

Chonnam National University Medical School in Gwangju acknowledged this in their study, noting that "changes in micronutrients could be linked with the other typical signs that precede dementia, including weight loss and low blood pressure.

(Source: http://news.bbc.co.uk/1/hi/health/7226872.stm)

Low blood concentrations of vitamin D may be associated with higher blood pressure in whites, indicating a risk of developing hypertension, or high blood that requires medical treatment, researchers report. However, this relationship was not noted among blacks.

"Though easily corrected by taking a vitamin D supplement or having causal sunlight exposure, vitamin D insufficiency is highly prevalent in the United States," Dr. Vin Tangpricha told Reuters Health.

Thousands of premature births could be prevented if the mothers took folic acid for at least a year before getting pregnant, doctors have found.

A major study has shown that extra supplies of the B vitamin cut the risk of premature babies by 50 to 70 per cent.

ISLAMABAD: Mothers with low levels of vitamin B12 in their blood are at increased risk of having an infant with spina bifida -- a birth defect in which the spinal cord fails to form properly, Dutch researchers report.

(http://www.onlinenews.com.pk/details.php?id=123929)

WASHINGTON, Jan 28 (Reuters) - African immigrants with low levels of vitamin D are much more likely to be infected with tuberculosis, a finding that suggests the vitamin may help prevent and treat TB, Australian researchers said on Monday.

(http://www.reuters.com/article/latestCrisis/idUSN28469425)

NEW YORK (Reuters Health) - A person's level of vitamin C may predict his or her likelihood of having a stroke, according to a long-term study of some 20,000 middle-aged and older residents of Norfolk, United Kingdom

(http://www.reuters.com/article/healthNews/idUSCOL27365920080122)