I recently had a high PSA scare and started taking turmeric (curcumin) and several other anti-inflammatories. You can read about it if you are in a similar situation in my page on My Elevated PSA with No Cancer. During this time I had to go off HRT which dropped my testosterone from a peak of about 1200 ng/dl to 111 ng/dl in less than a month. What I noticed, though, was that there was little effect on my erectile strength. Of course, that made me wonder if the turmeric was somehow protective.
This would be surprising, though, because turmeric is not really known for stimulating nitric oxide or dropping blood pressure significantly. (There is one study on hypertensive rats that shows it can drop blood pressure in that case. ) However, after doing a little research, I found something interesting: turmeric has research strongly suggesting that it improves almost every major cardiovascular risk factor. And, of course, anything that improves your arteries is very likely going to improve your erections.
Here are Ten Ways That Turermicc (Curcumin) Extracts Can Improve Erectile Dysfunction:
1. Raises HDL. Turmeric (curcumin) increased HDL by 29% in one human study using 500 mg/day.  This is a substantial increase and would take you months or years of cardiovascular training to achieve. Of course, you should still do the cardio, but my point is that this seems to have incredible powers in this area.
2. Increase Plasma Nitric Oxide. One study found that plasma nitric oxide was increased in "in healthy middle aged people (40-60 years old) with a low dose of curcumin (80 mg/day) in a lipidated form expected to have good absorption." 
3. Lowers Cholesterol. The same study that showed an increase in HDL also showed a drop in cholesterol of about 12%.  Remember: both small and large particle LDL particales can contribute to arterial plaque and so any non-statin lowering of LDL numbers is likely to help you. (Statins decrease CoQ10 and increase arachidonic acid.)
4. Antioxidant Strength. One of the processes that contributes to arteriosclerosis is the oxidation of LDL and turmeric, at least in an animal study, reduced this destructive process. 
CAUTION: I'm not sure how much of an effect this is, but there is study out there that shows that turmeric extract can lower ferritin. Low ferritin men may want to do some research and discuss with their physician.
5. Fibrinogen. One of the less known but most deadly cardiovascular risk factors is fibrinogen. This blood chemical increases the risk of clotting, which is, of course, a key step in both stroke and heart attacks. One study showed that even small amounts of turmeric dropped fibrinogen levels "like a rock" in partipants with elevated fibrinogen. 
6. Arteriosclerosis Prevention . The researchers who conducted the study for #3 did an additional study and found that both HDL and LDL oxidation were again signicantly lowered in those with high levels.  Their conclusions? "This preliminary experiment suggests that the Curcuma phenolic antioxidants, because of their high antioxidant activity and lack of toxicity, might be a useful complement to standard hypo-lipidemic drugs in the prevention and treatment of atherosclerosis." Of course, no one listens on this side of the ocean, because it's not an expensive pharmaceutical solution!
7. Arterial Protection Against Hypertension. High blood pressure is very hard on the walls of your arteries and can lead to stiffening and hardening. One study showed that curcumin likely protects against both. 
8. Arterial Protection Against Nitric Oxide Deficiency. How many of us middle-aged guys that have eaten a Western Diet all of our lives have nitric oxide deficiency? Well, I do know that Dr. Nathan Bryan said most of us have less than half of our nitric oxide by age 50. I don't know the exact definition of NO deficiency, but the lion's share of us are very low and one animal study showed that turmeric protects against the oxidation, hypertension and loss of elasticity that occurs when nitric oxide drops significantly. 
9. Arterial Protection Against Homocysteine. Homocysteine is yet another risk factor for the cardiovascular systems that has received a lot of air time lately. And, yes, turmeric protects against its effects as well. 
10. Lowers Triglycerides. The same study that showed that turmeric could increase plasma nitric oxide also found that it lowered triglyceride levels as well. 
So what is the pattern? If you'll notice, turmeric is, in my opinion, the perfect compliment to many of the nitric oxide-boosting supplements that you are already probably consuming. Let me explain why:
Many of the research-backed supplements - Korean Ginseng, Pycnogenol, Citrulline, Icariin, etc - increase nitric oxide directly (or indirectly through action on eNOS) - but do not actually protect your arteries or cardiovascular system from damage. Turmeric helps those arteries stay supple and softened and un-hardened. Stiff arteries cannot expand and allow increased blood flow and that includes the ones in your penis. This is where turmeric comes in: it helps keep your arteries youthful, at least according to all the above research.
Of course, you cannot eat horrendously, sleep little, smoke, be sedentary and expect turmeric to magically protect you. But, for those making the effort, turmeric is a nice insurance policy.
There is also evidence that turmeric will keep you alive and "in the game" in a hundred other ways: it protects, prevents and sometimes even helps with arthritis, IBS, prostate cancer, (some forms of) prostatitis, Alzheimer's, enlargement of the heart, diabetic neuropathy - the list just goes on and on. Basically, every guy knows that offense brings in the crowds, but you win games with a good defense, eh?
CAUTION: Of course, multigrams of turmeric are eaten regularly - daily in many cases - in Asian cultures all over the world and side effects are quite rare. This gives turmeric one of the most safe and undisputed anti-inflammatory records of all the superfoods. That said, it can increase oxalates according to one study and thus could potentially increase the risk of a kidney stone in sensitive individuals. It also does effect one of the liver enzyme systems somewhat and so it is a good idea to check with your doctor if you are on any medications.
1) Indian Journal of Physiology and Pharmacology, 1992, 36(4):273-275, "Effect of oral curcumin administration on serum peroxides and cholesterol levels in human volunteers"
2) Atherosclerosis, Dec 1999, 147(2):371 378, "Oral administration of a turmeric extract inhibits LDL oxidation and has hypocholesterolemic effects in rabbits with experimental atherosclerosis"
4) July 1997, 20(3): 165-168, "Effects of the antioxidant turmeric on lipoprotein peroxides: Implications for the prevention of atherosclerosis"
5) Nutrition & Metabolism 2011, 8:72, "Spice up the hypertension diet - curcumin and piperine prevent remodeling of aorta in experimental L-NAME induced hypertension"
6) Hypertension Research, 2012, 35:418 425, "Tetrahydrocurcumin alleviates hypertension, aortic stiffening and oxidative stress in rats with nitric oxide deficiency"
7) International Journal of Cardiology, Apr 2009, 133(2):145-151, The protective role of curcumin in cardiovascular diseases"
8) Journal of Vascular Surgery, Dec 2004, 40(6):1216 1222, "Curcumin blocks homocysteine-induced endothelial dysfunction in porcine coronary arteries"
9) Zhongguo Ying Yong Sheng Li Xue Za Zhi, 2006 Aug,22(3):257-61, "Effect of curcumin on pulmonary hypertension and wall collagen of pulmonary arterioles of chronic hypoxic hypercapnic rats"
10) Nutr J, 2012 Sep 26, 11:79, "Diverse effects of a low dose supplement of lipidated curcumin in healthy middle aged people"