If I take a multivitamin, is there a benefit to taking a supplement of a specific vitamin (ex. Vitamin D)? In the winter, I have read taking Vitamin D helps give more energy. I find myself more tired and depressed in winter months.
There are some studies that link low vitamin D levels with various issues, such as "winter depressions", but it should be remembered that this does NOT mean that vitamin D supplements will make you less depressed or give you more energy. It's just as plausible that the lack of light during the winter makes you both depressed AND results in lower vitamin D levels. Adding vitamin D doesn't make the sun come out, so to speak :)
Vitamin D supplementation had no overall effect on depressive symptoms (standardized mean difference [SMD], 0.14; 95% confidence interval [CI], -0.33 to 0.05, p = .16), although considerable heterogeneity was observed. Subgroup analysis showed that vitamin D supplementation for participants with clinically significant depressive symptoms or depressive disorder had a moderate, statistically significant effect...
There are some studies refered to in this link that should convince you to not waste money on Vitamin D: https://skeptics.stackexchange.com/questions/18322/do-vitamin-d-supplements-help-against-winter-depression
The same is almost definitely true about any other vitamins you are taking as well, unless you eat VERY bad, you probably don't have any deficiencies.
Winter sucks, I know, go for a walk during the lighter hours if possible, it's free, healthy and much more likely to make you feel better.