There are a number of treatments for the last. I already use melatonin. I sort of have light therapy from a full-spectrum fluorescent desk lamp. But I get very little sunlight; the surprising thing would be if I didn’t have a vitamin D deficiency. And vitamin D deficiencies have been linked with all sorts of interesting things like near-sightedness, with time outdoors inversely correlating with myopia and not reading or near-work time. (It has been claimed that caffeine interferes with vitamin D absorption and so people like me especially need to take vitamin D, on top of the deficits caused by our vampiric habits, but I don’t think this is true35.) Unfortunately, there’s not very good evidence that vitamin D supplementation helps with mood/SAD/depression: there’s ~6 small RCTs with some findings of benefits, with their respective meta-analysis turning in a positive but currently non-statistically-significant result. Better confirmed is reducing all-cause mortality in elderly people (see, in order of increasing comprehensiveness: Evidence Syntheses 2013, Chung et al 2009, Autier & Gandini 2007, Bolland et al 2014).

Research in animals shows that blueberries may help protect the brain from the damage caused by free radicals and may reduce the effects of age-related conditions such as Alzheimer's disease or dementia. Studies also show that diets rich in blueberries improved both the learning and muscle function of aging rats, making them mentally equal to much younger rats.
Speaking of addictive substances, some people might have considered cocaine a nootropic (think: the finance industry in Wall Street in the 1980s). The incredible damage this drug can do is clear, but the plant from which it comes has been used to make people feel more energetic and less hungry, and to counteract altitude sickness in Andean South American cultures for 5,000 years, according to an opinion piece that Bolivia’s president, Evo Morales Ayma, wrote for the New York Times.
Farah questions the idea that neuroenhancers will expand inequality. Citing the "pretty clear trend across the studies that say neuroenhancers will be less helpful for people who score above average", she said that cognitive-enhancing pills could actually become levellers if they are dispensed cheaply. A 2007 discussion paper published by the British Medical Association (BMA) also makes this point: "Selective use of neuroenhancers among those with lower intellectual capacity, or those from deprived backgrounds who do not have the benefit of additional tuition, could enhance the educational opportunities for those groups." If the idea of giving a pill as a substitute for better teaching seems repellent - like substituting an IV drip of synthetic nutrition for actual food - it may be preferable to a scenario in which only wealthy kids receive a frequent mental boost.
When I worked on the Bulletproof Diet book, I wanted to verify that the effects I was getting from Bulletproof Coffee were not coming from modafinil, so I stopped using it and measured my cognitive performance while I was off of it. What I found was that on Bulletproof Coffee and the Bulletproof Diet, my mental performance was almost identical to my performance on modafinil. I still travel with modafinil, and I’ll take it on occasion, but while living a Bulletproof lifestyle I rarely feel the need.

The use of cognition-enhancing drugs by healthy individuals in the absence of a medical indication spans numerous controversial issues, including the ethics and fairness of their use, concerns over adverse effects, and the diversion of prescription drugs for nonmedical uses, among others.[1][2] Nonetheless, the international sales of cognition-enhancing supplements exceeded US$1 billion in 2015 when global demand for these compounds grew.[3]