That sounds suspiciously like improved quality of life aka improved health span - which sounds good to me - even if I break on schedule
You're falling into the usual trap around the healthspan construction, which is to imagine that it will mean that we will have an extended period of healthiness and then just drop dead of ill-defined asymptomatic mechanisms. Pushing harder on the gas pedal so that the damaged engine pushes runs faster means that the car is still progressively getting worse, not that you "get to" speed into a cliff with no prior engine problems.
Which blood markers though? Reports from older individuals, 70 and up, on the experience threads should be better than they are, were it to improve blood flow and exercise capacity as theorized. Sinclairs mice seem to respond better but then again mice rarely if ever translate (making them almost useless as a model imo).
I would here invoke Winston Churchill's comments about democracy being the worst of all possible systems of government — except for all the alternatives.
I see it more as putting a turbocharger on a worn engine. It will likely provide a boost for a while, but might not be good long term, depending on how worn the engine is, and how much you turn up the boost.
I'd say that's really just another phrasing of the same metaphor.
The sublingual method bypasses the liver (partly), to deliver it where used elsewhere.
... in theory. We have zero pharmacokinetic data: for all we know, the NMN in those tabs just gets degraded in the mouth, or trickles down your throat instead of going as a bolus to the stomach — let alone pharmacodynamics, which is what's really of interest.
Kind of like fixing the spark plugs, or wires, or other parts of the engine downstream from the carburetor.
You wouldn't be fixing anything — you'd just be avoiding one of many damaged parts in favor of others. However, I'd agree that there is a theoretical advantage of bypassing the liver even in the young, and more so in the old if the local conversion to NAM and metabolites is even greater.
I agree with Oakmans theories about the exercise also. The muscles use the NAD+, and activate AMPK, which increases NAMPT, in a virtuos cycle. But we know older folks don't get benefit from exercise when they don't have sufficient NAD+.
Careful. Old people and mice most certainly do benefit from exercise, despite their lower NAD levels (and perhaps one of the reasons they do is exactly by upregulating NAMPT); Sinclair's study and others, as well as theory, does certainly suggest that you'll get better performance out of exercise with NAD+ boosting or reduced disposition, and I'd agree with you that there's a plausible case that they get more actual benefit as well (above & beyond that directly attributable to the performance boost).
Sinclair study found far more benefit with NMN and exercise combined than either alone.
In fact, it even found the young mice who exercised had much benefit from NMN.
Dumping extra, uneeded NAD+ on young, lazy mice had no benefit, and might build up the NAM/MeNam over time. But exercise them, and they do indeed become "supermice".
So in my thinking, smaller sublingual dosages along with exercise spares the massive overload in the liver which results in build up of downstream metabolites that the body cant quite process fast enough.
That's a quite intriguing hypothesis. I'd add more explicitly that it might also reduce the downstream buildup of metabolites in the muscles themselves, by allowing more NAM to be recycled back to NAD+ by boosting NAMPT.