You want the best health and well-being for yourself and loved ones, but vitamins and supplements, are no panacea.  Furthermore, know that the law does not require proof they work. And, overdoses and conflicts with real medicines do occur (so they cannot be taken with impunity).  Nevertheless, well-designed studies do indicate a modest benefit.  Here's one, for instance, that states:

14 641 middle-aged and older men were studied during a mean of 11 years of treatment and follow-up to determine if a multivitamin supplement taken daily can affect the risk of cancer. 

Findings:

Daily multivitamin use was associated with a reduction in total cancer among 1312 men with a baseline history of cancer (HR, 0.73; 95% CI, 0.56-0.96; P = .02), but this did not differ significantly from that among 13 329 men initially without cancer (HR, 0.94; 95% CI, 0.87-1.02; P = .15; P for interaction = .07).

Findings Translated:

"Although the main reason to take multivitamins is to prevent nutritional deficiency, [our study's] data provide support for the potential use of multivitamin supplements in the prevention of cancer in middle-aged and older men."

Gaziano JM, MD, Sesso HD, Christen WG, et al. "Multivitamins in the Prevention of Cancer in Men;The Physicians' Health Study II Randomized Controlled Trial."

However, you would never hire the fox to watch over the chicken coop, would you? 

What this means in this context is that you cannot expect the vitamin and supplement industry to be completely open and transparent; it's not in their best interest.  After all, they have a deep, financial interest in selling their products AND they are not required to prove what they sell is A) safe, B) pure, C) effective or D) harm-free. Moreover, "despite their popularity, there is no evidence that multivitamins enhance health or prevent illness. In fact, both the U.S. Preventive Services Task Force and a National Institutes of Health State-of-the-Science Conference concluded that multivitamins do not offer protection against heart disease or cancer. In contrast, research suggests that fish oil supplements may be beneficial for people with heart disease."

For further information:

Office of Dietary Supplements

Food and Drug Administration

National Center for Complementary and Alternative Medicine

Main Reference:

"Do vitamins and other supplements live up to their promise?" Harvard Men's Health Watch," April 2012

 

As one English professor of mine at the Children's Hospital of Philadelphia said, Americans have the most expensive urine in the world. Neverthless, I can recommend 1000 mg Vit D/day, and ample fish oil and fiber.

Here's the latest scoop, for instance, on Vitamin D:

It does seem to have an effect on immune function, but to what extent? (Is this just another probiotics-like debacle?)

We get about 90% of our vitamin D* via sunlight and the rest comes from diet—egg yolk, oily fish and vitamin D fortified dairy products. How, then, does one explain that more than half of people living in places where there's a lot of exposure to sunshine, like Hawaii, have lab values that declare they are deficient in vitamin D?

Regarding asthma (reactive airway disease) and allergies, observational studies are inconclusive. Here's one such study, but first and last, why there was no clear definition of what is a normal circulating vitamin D level, control group, control for socioeconomic status differences, or crossover design.

Serum vitamin D levels are inversely related to markers of allergies—serum total IgE levels and eosinophilia counts, and reactive airway disease manifestations—airway hyperresponsiveness, and/or hospitalizations for asthma, but not the gold standard, the mean forced expiratory volume in 1 second. How can that be?

One Study's Highlights

• The study participants were 616 asthmatic Costa Rican children between the ages of 6 and 14 years of age.


• Researchers adjusted the study results to account for potential confounders— body mass index, age, sex, and parental educational levels.


• 91% of participants had an unscheduled medical visit for asthma in the past year. Nevertheless, only 39% had received the mainstay of asthma treatment in the last year, which is the use of an anti-inflammatory medication.


• Findings: As defined above, 3.4% of participants had vitamin D deficiency; 24.6% were vitamin D insufficient.


• The more the serum vitamin D levels, the lower some of the markers of allergy: i.e., less airway hyperresponsiveness on methacholine challenge tests; less dust mite skin test reactivity; lower risk for hospitalization for asthma in the previous year; for each 10-ng/mL increase in 25(OH)D levels in an average male subject, serum total IgE levels fell by 25 IU/mL; eosinophil counts fell by 29 cells/m3


• Finally, in full confirmatory analysis, vitamin D levels were unrelated to the use of anti-inflammatory medications. Reference: Am J Respir Crit Care Med. May 1, 2009;179:739-742, 765-771.

[* Vitamin D deficiency herein was defined as levels of 25(OH)D less than 20 ng/mL, and levels between 20 and 30 ng/mL indicated insufficient vitamin D.]

In the same Journal, Graham Devereux, MD (Aberdeen, UK) said: "Studies that supplement with the currently recommended doses of vitamin D, while unlikely to raise ethical or regulatory concerns, would fail to address the scientific evidence that larger vitamin D intakes (e.g., 2,000 IU/d) may be required for beneficial nonskeletal effects.... While these concerns may be satisfactorily addressed, it remains to be seen whether pregnant women, parents, or patients will be similarly convinced and participate in such studies. Ultimately, it is only by investigating the effects of vitamin D in doses at, and above those currently recommended, that decisions can be made on the optimal intake of vitamin D for health and the possible prevention and treatment of asthma."

 

Regardless, the final word even about vitamin D is not in. Just remember, there's no free lunch, but judicious use of sunlight—why not?