Researchers have recently uncovered a sobering fact that health-seeking men everywhere should be interested in: too many antioxidants could potentially be bad for the heart and cardiovascular system. Of course, the conventional wisdom is that antioxidants are always good, because they quench the overabundance of free radicals and oxidation that plagues and ages us as through the passing decades.
However, scientists found that some free radicals actually do important work and play critical roles in human tissues and one of those molecules is hydrogen peroxide. It turns out that the same stuff that can clean a wound, due to its oxidative superpowers, also helps dilate your arteries.  The primary researchers of this subject are David Poole and Timothy Musch, K-State professors from the Cardiorespiratory Exercise Laboratory. They have done a number of studies showing that anything that overly quenches H2O2 could potentially be bad for both heart and arterial health by limiting the ability of your arteries and vessels to relax. 
Of course, as men we are intimately interested in anything that might constrict the arteries in the penis, eh? This has the potential to affect not just our sex lives, however, but our existence if it disturbs the heart muscle itself. Exercise performance and brain function could be disturbed somewhat as well. One study on rats looked used just two antioxidants, including Vitamin C, and found that muscle tissue was actually affected by the decrease in hydrogen peroxide and ensuing vasocontriction. 
Sounds scary, right? Not really when you consider that the rats were actually fed an IV of Vitamin C and tempol, an SOD-like molecule. NOTE: SOD is arguably your body's most powerful and important antioxidant. So, while theoretically interesting, this is anythng but a natural situation. What this study really shows is that perhaps megadosing on antioxidant supplements is an idea that deserves some caution. But my concern is that men will read these studies and conclude that consumption of dietary antioxidants is somehow dangerous or risky.
NOTE: I discuss this study and several others in my link on The Dangers of Antioxidant Supplements that show that these supplements, at best, are poorly understood and may even cause more harm than good.
Clearly, the studies show that dietary antioxidants are a good thing and will help your cardiovascular system and long term health in many ways. Some researchers have rightly pointed out that, when we get our antioxidants from whole plant foods, that we ingest many antioxidants in reasonable levels that can protect various cell lines and tissues in varied and multi-faceted way. 
And the proof comes from the fact that both a Low Fat Diet, which is generally high in plant foods and, therefore antioxidants, lowers blood pressure and increases blood flow. There is no vasoconstrition going on with these diets - quite the opposite! So, yes, you may want to think twice about megadosing on antioxidant supplements, but this does not seem to apply to the healthy diets known to epidemiologists and researchers.
Most of the healthy supercultures in the world eat an abundance of dietary antioxidants from fruit, vegetables and sometimes whole grains. And they enjoy extraordinary good health and blood pressure throughout their lives. Clearly consuming dietary antioxidants does not cause too many problems since these people have virtually no heart disease or hypertension. (See my Review of Healthy at 100 for some examples of the supersupercultures.)
There are dozens of studies showing the benefits of antioxidants from dietary sources and here are just a few:
1. Protection Against a High Fat Meal. One study showed that eating a higher antioxidant meal helped protect participants from the nasty effects of a high fat meal. 
2. Protection Against Dementia. Low betacarotene levels (from food) were associated with increased risk for dementia in seniors. 
3. Bronchial Reactivity. Vitamin C in the diet was linked to "bronchial reactivity" in children, leaving them vulnerable to various upper respiratory conditions. 
4. Coronary Heart Disease. A study in Lancet of seniors showed that levels of Vitamins C and E and betacarotene in the diet were correlated with heart disease.  The reasons for this are probably due to multiple pathways, but the primary cause is that dietary antioxidants can actually prevent or slow down the oxidation of LDL cholesterol, which play a major role in the buildup of arterial plaque and hardening of the arteries.  One big study on women found that Vitamin E intake from diet was particularly strongly associated with lower rates of cardiovascular disease. 
Again, the list of studies could go on and on, but a meta-analysis summarized it best:
"At this time, the scientific evidence supports recommending consumption of a diet high in food sources of antioxidants and other cardioprotective nutrients, such as fruits, vegetables, whole grains, and nuts, instead of antioxidant supplements to reduce risk of CVD." 
Now none of these proves that there was no vasoconstriction going on in some cases. However, clearly vasoconstriction does not seem to be any kind of significantl factor based on literally dozens of different studies such as these. Why would asthma, heart disease and dementia risks - all dependent on and associated with blood flow in many ways - do so well with dietary antioxidants if dietary antioxidants are a health issue and restrict blood flow? It just does not make sense.
And, again, why is increased fruit, vegetable and whole grain consumption associated with decreased blood pressure in patients with hypertension if antioxidants are quenching hydrogen peroxide. Read about the DASH Diet, which is currently one of the common recommendations by the medical profession for high blood pressure: it's core is a plant-based diet loaded with antioxidants.
The bottom line is always: eat a whole foods, low glycemic, primarily plant-based diet rich in antioxidants and anti-inflammatories for maximum health and sexual function. Study after study has show that this is the way to go.
NOTE: You may be interested to know that some antioxidants have been shown to boost testosterone (in large doses). See my link on Antioxidants and Your Testosterone for more information.
2) J Am Coll Cardiol,Epub 2007 Sep 10, 2007 Sep 25, 50(13):1272-8, "Important role of endogenous hydrogen peroxide in pacing-induced metabolic coronary vasodilation in dogs in vivo"
3) Experimental Physiology, Sep 2009, 94(9):961-971, The effects of antioxidants on microvascular oxygenation and blood flow in skeletal muscle of young rats"
5) Am J Clin Nutr, Jan 2003, 771(1):139-143, "Effect of dietary antioxidants on postprandial endothelial dysfunction induced by a high-fat meal in healthy subjects"
6) QJM, 1999, 92(9):527-530, "Interaction of dietary antioxidants in vivo: how fruit and vegetables prevent disease?"
7) Am J Epidemiol 1996; 144:275ï¿½80, "Dietary Antioxidants and Cognitive Function in a Population-based Sample of Older Persons The Rotterdam Study"
8) Thorax, 1997;52:166-170, , "Bronchial reactivity and dietary antioxidants"
9) Lancet, 23 Oct 1993, 342(8878):1007ï¿½1011, "Dietaryantioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study"
10) Arteriosclerosis, Thrombosis, and Vascular Biology, 1998; 18:1506-1513, "Dietary Antio11) N Engl J Med, 1996, 334:1156-1162, "Dietary Antioxidant Vitamins and Death from Coronary Heart Disease in Postmenopausal Women"
11) N Engl J Med, 1996, 334:1156ï¿½1162, "Dietary antioxidant vitamins and death from coronary heart disease in postmenopausal women"
12) Circulation, 2004; 110:637-641, "Antioxidant Vitamin Supplements and Cardiovascular Disease"